Ch 34 & 35 lecture
-
Upload
roy-withers -
Category
Education
-
view
28 -
download
2
Transcript of Ch 34 & 35 lecture
Copyright © 2009 Pearson Education, Inc..
Lectures by
Gregory AhearnUniversity of North Florida
Chapter 34-35
Nutrition, Digestion, and
Excretion
Copyright © 2009 Pearson Education Inc.
34-35.1 How Do Animals Regulate The Composition Of Their Bodies? A nutrient is any substance that an animal
needs but cannot synthesize or produce in its own body, and hence must acquire it from its environment as it eats or drinks.
Digestion is the process whereby an animal physically grinds up and chemically breaks down its food, producing small, simple molecules that can be absorbed into the circulatory system.
Copyright © 2009 Pearson Education Inc.
34-35.1 How Do Animals Regulate The Composition Of Their Bodies? Nutrition includes taking food into the body,
converting it into usable forms, absorbing the resulting molecules from the digestive tract into the circulatory system, and using the nutrients in the animal’s own metabolism.
Excretion is the disposal of indigestible, toxic, or surplus materials.
Copyright © 2009 Pearson Education Inc.
34-35.2 What Nutrients Do Animals Need?
Animal nutrients fall into six major categories:• Lipids• Carbohydrates• Proteins• Minerals• Vitamins• Water
Copyright © 2009 Pearson Education Inc.
34-35.2 What Nutrients Do Animals Need?
The primary sources of energy are lipids and carbohydrates.• Energy is provided mostly from lipids,
carbohydrates, and to lesser extent, proteins.• Energy in food is measured in Calories.• A Calorie is the amount of energy needed to
raise the temperature of 1 gram of water by 1 degree Celsius.
• The average person at rest burns 1,550 Calories per day at rest.
Copyright © 2009 Pearson Education Inc.
34-35.2 What Nutrients Do Animals Need?
Copyright © 2009 Pearson Education Inc.
34-35.2 What Nutrients Do Animals Need?
Lipids include fats, phospholipids, and cholesterol.• Fats and oils are used primarily as a source of
energy.• Cholesterol is used to make cell membranes
and several hormones, including testosterone and estrogen.
• Essential fatty acids, such as linoleic acid, cannot be synthesized and must be obtained in the diet.
Copyright © 2009 Pearson Education Inc.
34-35.2 What Nutrients Do Animals Need?
Fats store energy in concentrated form.• In humans, energy is stored primarily as fat.• When more Calories are eaten than are used,
the excess fats, carbohydrates, and proteins are all converted to fat for storage.
• Fats has twice as much energy per unit weight as the other nutrients.
• Lipids are hydrophobic and do not cause water to be accumulated within the fats in the body.
Copyright © 2009 Pearson Education Inc.
34-35.2 What Nutrients Do Animals Need?
For example, the ruby-throated hummingbird migrates across the Gulf of Mexico in the fall, getting its energy from stored lipids.
Fig. 34-35-1
Copyright © 2009 Pearson Education Inc.
34-35.2 What Nutrients Do Animals Need?
Carbohydrates are a source of quick energy.• Carbohydrates include simple sugars and
longer chains of sugars called polysaccharides.
• During digestion, simple sugars, like glucose, are derived from the breakdown of more complex carbohydrates, such as sucrose and starch.
• Animals and humans store sugars as glycogen, a large branched chain of glucose molecules.
Copyright © 2009 Pearson Education Inc.
34-35.2 What Nutrients Do Animals Need?
Proteins provide amino acids for building new proteins.• Protein provides these amino acids after they
are digested.• Dietary protein comes from meat, milk, eggs,
corn, and beans.• Our bodies can synthesize certain amino
acids, but eight cannot be made by our biochemistry and must be supplied in our diet—they are called “essential amino acids”.
Copyright © 2009 Pearson Education Inc.
34-35.2 What Nutrients Do Animals Need?
Protein deficiency can cause a variety of debilitating conditions, including kwashiorkor.
Fig. 34-35-2
Copyright © 2009 Pearson Education Inc.
34-35.2 What Nutrients Do Animals Need?
Minerals are elements required by the body.• A mineral is a chemical element that is
required for proper bodily function.• Minerals are needed for strong bones and
teeth, for muscles contraction, for nerve functions, and for proper blood cell functions.
• Metals are also important since they act as parts of enzymes in certain body reactions (e.g., zinc, copper, selenium).
Copyright © 2009 Pearson Education Inc.
Copyright © 2009 Pearson Education Inc.
34-35.2 What Nutrients Do Animals Need?
Vitamins play many roles in metabolism.• Vitamins are a diverse group of organic
compounds that animals require in very small amounts.
• The body cannot synthesize them, so they must be obtained in the diet.
• Vitamins are grouped into two categories: water soluble and fat soluble.
Copyright © 2009 Pearson Education Inc.
Copyright © 2009 Pearson Education Inc.
Copyright © 2009 Pearson Education Inc.
34-35.2 What Nutrients Do Animals Need?
Water-soluble vitamins• These substances dissolve in water or blood
plasma and are excreted by the kidney; they therefore do not build up in the body.
• They include vitamin C and the B-vitamin complex.
Copyright © 2009 Pearson Education Inc.
34-35.2 What Nutrients Do Animals Need?
A deficiency in niacin, a B-vitamin, causes cracked, scaly skin and digestive and nervous system disorders.
Fig. 34-35-3
Copyright © 2009 Pearson Education Inc.
34-35.2 What Nutrients Do Animals Need?
Fat-soluble vitamins• Fat soluble vitamins can accumulate in the
body and be toxic if present in too high a concentration.
• This group includes:• Vitamin K: regulates blood clotting• Vitamin A: produces visual pigments in the
eyes for vision• Vitamin D: promotes strong bones• Vitamin E: prevents cellular damage; is an
antioxidant
Copyright © 2009 Pearson Education Inc.
34-35.2 What Nutrients Do Animals Need?
Vitamin D deficiency can lead to a condition called Rickets, which is a deterioration of bone.
Fig. 34-35-4
Copyright © 2009 Pearson Education Inc.
34-35.2 What Nutrients Do Animals Need?
The human body is about two-thirds water.• Water is the principal component of saliva,
blood, lymph, extracellular fluid, and cytoplasm within each cell.
• The average human requires about 2,500 milliliters (10 cups) of water per day, but this can change with exercise, temperature, and humidity.
• We obtain about half of our water from the food we eat and the rest is obtained from the fluids we drink.
Copyright © 2009 Pearson Education Inc.
34-35.2 What Nutrients Do Animals Need?
Nutritional guidelines help people obtain a balanced diet.• Nutritional guidelines, called “My Pyramid,”
are posted to a U.S. government interactive website.
• Other sources of nutritional information are found on the labels of commercially packaged foods; they contain information about calorie, fat, sugar, and vitamin content.
Copyright © 2009 Pearson Education Inc.
34-35.2 What Nutrients Do Animals Need?
Are you too heavy?• A simple way to calculate whether your
weight is likely to pose a health risk is to calculate your body mass index (BMI).
• The BMI takes into account your weight and height to arrive as an estimate of body fat.
• Two ways to calculate your BMI are:
1. Weight (in kilograms)/height2 (in meters)
2. Weight (in pounds) x 703/height2 (in inches)
Copyright © 2009 Pearson Education Inc.
34-35.2 What Nutrients Do Animals Need?
Are you too heavy? (continued)• A BMI between 18.5 and 25 is considered
healthy.• People with anorexia have a BMI of 17.5 or
lower.• A BMI between 25 and 30 indicates you are
probably overweight.• A BMI over 30 indicates your are obese.
Copyright © 2009 Pearson Education Inc.
34-35.3 What Are The Major Processes Of Digestion? All digestive systems must accomplish
certain tasks.• Ingestion: food is brought into the digestive
tract through the mouth• Mechanical breakdown: the physical
breakdown of food into small pieces• Chemical breakdown: digestive enzymes
convert the large molecules in food into small molecules
Copyright © 2009 Pearson Education Inc.
34-35.3 What Are The Major Processes Of Digestion? All digestive systems must accomplish
certain tasks (continued).• Absorption: the transfer of small molecules
across the gut to the blood and then to cells of the body
• Elimination: indigestible materials are expelled from the body
Copyright © 2009 Pearson Education Inc.
34-35.4 What Is The Diversity Of Digestive Systems In Non-Human Animals? In sponges, digestion occurs within single
cells.• Sponges rely exclusively on individual cells to
digest their food.• Sponges circulate seawater through pores in
their bodies, and collar cells filter microscopic organisms from the water and ingest them by phagocytosis.
• Phagocytized food is digested inside these cells in sacs called lysosomes, which contain digestive enzymes.
Copyright © 2009 Pearson Education Inc.
34-35.4 What Is The Diversity Of Digestive Systems In Non-Human Animals? Intracellular digestion in a sponge
Fig. 34-35-6
H2O carryingfood particlesenters the pores
Food particlesare filtered from thewater by the collar
Food enters thecollar cell by phagocytosis,forming a food vacuole
Waste products areexpelled by exocytosis
Water, uneaten food,and wastes are expelledthrough the large openingat one end of the sponge
collar cell
H2O
H2O
lysosomewithdigestiveenzymes
food vacuole
The foodvacuole mergeswith a lysosome
H2O
H2O
A simple sponge
Tube sponges
Collar cell(b)
(a)
(c)
Copyright © 2009 Pearson Education Inc.
34-35.4 What Is The Diversity Of Digestive Systems In Non-Human Animals? Jellyfish and their relatives have digestive
systems consisting of a sac with a single opening.• The most simple digestive tract occurs in sea
anemones, coral, and jellyfish, which possess a sac with one opening.
• Both food and waste pass through the single opening.
• Food is chemically broken down in the sac by digestive enzymes, and the nutrients are absorbed by cells lining the sac.
Copyright © 2009 Pearson Education Inc.
34-35.4 What Is The Diversity Of Digestive Systems In Non-Human Animals? Digestion in a sac
Fig. 34-35-7
Tentacles withstinging cells capturethe prey and carryit into the mouth
Gland cells secretedigestive enzymes intothe digestive sac andbegin extracellulardigestion
Nutritive cells engulffood particles andcomplete digestionwithin food vacuoles
mouth
prey
prey
digestivesac
Hydra with prey
Food processing in Hydra
(a)
(b)
Copyright © 2009 Pearson Education Inc.
34-35.4 What Is The Diversity Of Digestive Systems In Non-Human Animals? Most animals have digestive systems
consisting of a tube with several specialized compartments.• The tube performs different functions along its
length; food is first mechanically broken down, then chemically altered, then the nutrients are absorbed, and finally, wastes are eliminated.
Copyright © 2009 Pearson Education Inc.
34-35.4 What Is The Diversity Of Digestive Systems In Non-Human Animals? Worms, mollusks, arthropods, and
vertebrates are examples of animals with this type of gut.
Fig. 34-35-8
anus
intestine
pharynx
esophagus
mouth
crop gizzard
Soil withfood particlesis ingested
Indigestible remnantsare expelled
Food is digestedand absorbed in theintestine
Food is groundup in the gizzard
Copyright © 2009 Pearson Education Inc.
34-35.5 How Do Humans Digest Food?
Humans have a tubular digestive tract with several compartments in which food is broken down, physically and chemically, before being absorbed into the circulatory system.
Digesting and absorbing food requires coordinated action from the various structures of the digestive system.
Copyright © 2009 Pearson Education Inc.Fig. 34-35-9
Oral cavity. tongue,teeth: Grind food,mix with saliva
Stomach: Breaksdown food andbegins proteindigestion
Small intestine:Food is digestedand absorbed
Rectum: Stores feces
Salivary glands: Secretelubricating fluid andstarch-digesting enzymes
Pharynx: Shared digestiveand respiratory passage
Epiglottis: Directs fooddown the esophagus
Esophagus: Transportsfood to the stomach
Liver: Secretes bile (alsohas many non-digestivefunctions)
Gallbladder: Stores bilefrom the liver
Pancreas: Secretes buffersand several digestiveenzymes
Large intestine: Absorbsvitamins, minerals, andwater; houses bacteria;produces feces
Copyright © 2009 Pearson Education Inc.
34-35.5 How Do Humans Digest Food?
Breakdown of food begins in the mouth.• Mechanical food breakdown is due to the
action of 32 teeth of different shapes and sizes including incisors, canines, premolars, and molars.
• Three pairs of salivary glands secrete saliva, which lubricates the food, as well as amylase, which starts the chemical breakdown of sugars in the mouth.
Fig. 34-35-10
Copyright © 2009 Pearson Education Inc.
34-35.5 How Do Humans Digest Food?
Teeth begin the mechanical breakdown of food.
Fig. 34-35-10
incisors
canine
premolars
molars
Copyright © 2009 Pearson Education Inc.
34-35.5 How Do Humans Digest Food?
PLAYPLAY Animation—Digestion in the Mouth
Copyright © 2009 Pearson Education Inc.
34-35.5 How Do Humans Digest Food?
The pharynx connects the mouth to the rest of the digestive system.• With the help of the muscular tongue, the food
is manipulated into a mass and pressed backward into the pharynx, which connects the mouth with the esophagus.
• The swallowing reflex elevates the larynx, so that the epiglottis blocks off the opening to the trachea and guides food to the esophagus.
Copyright © 2009 Pearson Education Inc.
Before swallowing During swallowing
The epiglottis iselevated to allow airto flow through thepharynx into the larynx
The tonguemanipulatesfood whilechewing
Thetongue forcesfood into theesophagus
The larynx movesup and the epiglottisfolds over the larynx
pharynx
epiglottis
esophagus
larynx
roof of mouth
food
tongue
Food entersthe esophagus
food
esophagus
epiglottis
larynx
(a) (b)
34-35.5 How Do Humans Digest Food?
The challenge of swallowing
Fig. 34-35-11
Copyright © 2009 Pearson Education Inc.
34-35.5 How Do Humans Digest Food?
The esophagus conducts food to the stomach.• Swallowing forces food into the esophagus, a
muscular tube that propels the food from the mouth to the stomach.
• Muscles surrounding the esophagus produce a wave of contraction, called peristalsis, that begins above the swallowed food and progresses down the esophagus, forcing the food to the stomach.
Copyright © 2009 Pearson Education Inc.
34-35.5 How Do Humans Digest Food?
The stomach stores and breaks down food.• The human stomach is an expandable
muscular sac capable of holding as much as a gallon of food and liquids.
• The stomach has three functions:• It stores food and releases it gradually into
the small intestine for digestion and absorption.
• It assists in the mechanical food breakdown.
• It has a role in chemical food breakdown.
Copyright © 2009 Pearson Education Inc.
34-35.5 How Do Humans Digest Food?
PLAYPLAY Animation—Digestion in the Stomach
Copyright © 2009 Pearson Education Inc.
34-35.5 How Do Humans Digest Food?
Most digestion occurs in the small intestine.• The small intestine is 1 inch in diameter and
10 feet long.• It digests food into small molecules and
absorbs them into the bloodstream.• This process of digestion is accomplished with
the aid of secretions from the liver, the pancreas, and the cells of the small intestine itself.
Copyright © 2009 Pearson Education Inc.
34-35.5 How Do Humans Digest Food?
The liver and gallbladder provide bile.• The liver stores glycogen and detoxifies many
poisonous substances.• It also produces bile for digestion; bile is a
complex mixture of bile salts, other salts, water, and cholesterol.
• Bile is stored in the gallbladder and is released into the small intestine where it aids in fat digestion.
Copyright © 2009 Pearson Education Inc.
34-35.5 How Do Humans Digest Food?
The pancreas secretes digestive substances.• The pancreas consists of two major types of
cells:• One type produces hormones that regulate
blood sugar.• The other type produces a digestive
secretion called pancreatic juice; this contains water, sodium bicarbonate, and several digestive enzymes that break down sugars, lipids, and proteins.
Copyright © 2009 Pearson Education Inc.
34-35.5 How Do Humans Digest Food?
The intestinal wall completes the digestive process.• Digestive enzymes are embedded in the
plasma membrane of the cells that line the small intestine, so that the final phase of digestion occurs as the nutrient is being absorbed into the cell.
Copyright © 2009 Pearson Education Inc.
34-35.5 How Do Humans Digest Food?
Most absorption occurs in the small intestine.• The small intestine is the major site of nutrient
absorption into the blood.• It has numerous folds and projections that
give it an internal surface area 600 times greater than a smooth tube of the same length.
• Fingerlike projections called villi (singular, villus) cover the entire surface of the intestinal wall.
Copyright © 2009 Pearson Education Inc.
34-35.5 How Do Humans Digest Food?
Most absorption occurs in the small intestine (continued).• Each cell on a villus has microscopic
projections called microvilli, which increase the area for absorption even more.
• Within each villus is a network of blood capillaries and a single lymph capillary called a lacteal.
• Most nutrients pass through the cells of the small intestine and enter the capillaries, but breakdown products of fats pass across the cells and enter the lacteals.
Copyright © 2009 Pearson Education Inc.
34-35.5 How Do Humans Digest Food?
The small intestine
Fig. 34-35-12
villi
lacteal
arteriole
lymphvesselvenule
capillaries
microvilli
intestinalgland
fold ofintestinallining
Small intestine A fold of theintestinal lining
A villus Cells of a villus(a) (b) (c) (d)
Copyright © 2009 Pearson Education Inc.
34-35.5 How Do Humans Digest Food?
The large intestine absorbs water, minerals, and vitamins, and forms feces.• The large intestine in an adult human is about
5 feet long and 3 inches in diameter; the first part is called the colon and the last 6 inches is the rectum.
• Bacteria in the colon synthesize vitamin B12, thiamin, riboflavin, and vitamin K.
• Large intestine cells absorb water, minerals, and vitamins.
• Feces is formed in the large intestine.
Copyright © 2009 Pearson Education Inc.
34-35.5 How Do Humans Digest Food?
PLAYPLAY Animation—Digestion in the Intestines
Copyright © 2009 Pearson Education Inc.
34-35.5 How Do Humans Digest Food?
PLAYPLAY Animation—Absorption of Nutrients
Copyright © 2009 Pearson Education Inc.
34-35.5 How Do Humans Digest Food?
Digestion is controlled by the nervous system and hormones.• The secretions and muscular activity of the
digestive tract are regulated by both nerves and hormones.
• Sensory signals initiate digestion.• The sight, smell, taste, and just the thought
of food generate signals from the brain that act on the digestive tract.
• For example, nerve impulses stimulate the salivary glands and cause the stomach to secrete acid and mucus.
Copyright © 2009 Pearson Education Inc.
34-35.5 How Do Humans Digest Food?
Hormones help regulate digestive activity through negative feedback.• Gastrin is secreted from stomach cells in
response to the presence of protein breakdown products, and stimulates acid secretion by the stomach.
• Secretin and cholecytokinin are secreted by the small intestine in response to chyme coming from the stomach; they stimulate the secretion of digestive enzymes and sodium bicarbonate by the pancreas and bile from the liver.
Copyright © 2009 Pearson Education Inc.
34-35.5 How Do Humans Digest Food?
Gastric inhibitory peptide, secreted by the small intestine in response to fatty acids and sugars in chyme, stimulates the pancreas to release insulin.
This in turn stimulates body’s cells to absorb sugar from the blood.
It also inhibits stomach peristalsis, which slows its emptying rate.
Copyright © 2009 Pearson Education Inc.
34-35.6 What Are The Functions Of Urinary Systems? All urinary systems of animals function
similarly.• First, the blood is filtered, with water and small
dissolved molecules moving from the blood into the urinary system.
• Next, nutrients are selectively reabsorbed back into the blood.
• Some highly toxic substances are actively secreted from the blood into the urinary system.
• Finally, wastes and excess nutrients are excreted from the body.
Copyright © 2009 Pearson Education Inc.
34-35.7 What Is The Diversity Of Urinary Systems In Non-Human Animals? In a few animals, like sponges, individual
cells dump wastes into the surrounding water.
Most animals have complex urinary systems, under nervous and hormonal control, that regulate which substances are excreted and which are retained in the body’s fluids.
Flame cells are urinary structures in flatworms, while nephridia have the same role in earthworms.
Copyright © 2009 Pearson Education Inc.
34-35.7 What Is The Diversity Of Urinary Systems In Non-Human Animals? Flame cells filter fluids in flatworms.
• Because flatworms largely live in freshwater, a major function of their excretory system is to regulate water balance.
• The flatworm’s excretory system consists of a network of tubes that branch throughout the body.
• At intervals, the branches end blindly in single-celled bulbs called flame cells.
• Water and dissolved substances are filtered from the body by these bulbs, and are expelled through pores on the body surface.
Copyright © 2009 Pearson Education Inc.
flamecell
cilia
fluid
tubule
eyespot
excretorypores
34-35.7 What Is The Diversity Of Urinary Systems In Non-Human Animals? The simple
excretory system of a flatworm
Fig. 34-35-13
Copyright © 2009 Pearson Education Inc.
34-35.7 What Is The Diversity Of Urinary Systems In Non-Human Animals? Nephridia filter fluids in earthworms.
• Earthworms, mollusks, and other invertebrates have simple filtering structures called nephridia, which resemble the filtering structures found in vertebrate kidneys.
• Each segment of the worm contains a pair of nephridia that filter each segment of wastes and nutrients.
• The resulting urine is stored in a bladder-like portion of the nephridium and is excreted through pores in the body wall.
Copyright © 2009 Pearson Education Inc.
nephridia
intestine
excretory porenerve cord
34-35.7 What Is The Diversity Of Urinary Systems In Non-Human Animals? The excretory
system of the earthworm
Fig. 34-35-14
Copyright © 2009 Pearson Education Inc.
34-35.8 How Does The Human Urinary System Work? The human urinary system produces,
transports, and excretes urine.• The kidneys are organs in which the fluid
portion of the blood is collected and filtered.• From this fluid, water and important nutrients
are then reabsorbed into the blood.• The remaining fluid, called urine—consisting
of toxic substances, cellular waste products, excess vitamins, salts, some hormones, and water—stays behind and is excreted from the body.
Copyright © 2009 Pearson Education Inc.
34-35.8 How Does The Human Urinary System Work? The urinary system is crucial for
homeostasis.• It regulates blood levels of ions such as
sodium, potassium, chloride, and calcium.• It regulates the water content of the blood.• It maintains proper pH of the blood.• It retains important nutrients such as glucose
and amino acids in the blood.• It eliminates cellular waste products such as
urea.
Copyright © 2009 Pearson Education Inc.
ammonia
urea
carriedin blood
carriedin blood
amino acid
In cells, amino acidsare broken into simplermolecules, releasingammonia
In the liver, ammoniais converted to urea
In the kidneys, urea andother water-soluble wastesare filtered from the blood
excretedin
urine
34-35.8 How Does The Human Urinary System Work? A flow diagram
showing the formation and excretion of urea
Fig. 34-35-15
Copyright © 2009 Pearson Education Inc.
34-35.8 How Does The Human Urinary System Work? The urinary system consists of the kidneys,
ureter, urinary bladder, and urethra.• Human kidneys are paired organs located on
either side of the spinal cord, slightly above the waist.
• The kidneys produce urine, which leaves each kidney through a narrow, muscular tube called a ureter.
• The ureters transport the urine to the urinary bladder.
• The urethra is a short tube from the bladder to the outside world.
Copyright © 2009 Pearson Education Inc.
34-35.8 How Does The Human Urinary System Work? The human urinary
system
Fig. 34-35-16
left renalartery
left kidney
left renalveinaorta
left ureter
urinarybladder
urethra(in penis)
vena cava
Copyright © 2009 Pearson Education Inc.
34-35.8 How Does The Human Urinary System Work?
PLAYPLAY Animation—Human Urinary System
Copyright © 2009 Pearson Education Inc.
34-35.8 How Does The Human Urinary System Work? Urine is formed in the nephrons of the
kidneys.• Each kidney contains a solid outer layer
where urine forms and an inner chamber that collects urine and funnels it into the ureter.
• The outer layer of each kidney contains about a million tiny tubes called nephrons, which filter the blood, process the filtered fluid, and form urine.
Copyright © 2009 Pearson Education Inc.
34-35.8 How Does The Human Urinary System Work? Cross section of a
kidney
Fig. 34-35-17
renalartery
renalvein
ureter(cut awayto showthe pathof urine)
tobladder
renal pelvis(cut awayto show thepath of urine)
urine
collectingduct
nephron
enlargement of a singlenephron and collecting duct
Copyright © 2009 Pearson Education Inc.
34-35.8 How Does The Human Urinary System Work? Each nephron has three parts:
• The glomerulus: capillaries from which fluid is filtered from the blood and collected
• Bowman’s capsule: captures filtered fluid from the glomerulus
• The tubule: receives filtered fluid from Bowman’s capsule
Copyright © 2009 Pearson Education Inc.
34-35.8 How Does The Human Urinary System Work? An individual
nephron and its blood supply
Fig. 34-35-18
collectingduct
distal tubule
proximal tubule
glomerulus
Bowman’scapsule
arterioles
branch ofrenal vein
branch ofrenal artery
loop of Henle
capillaries
Copyright © 2009 Pearson Education Inc.
34-35.8 How Does The Human Urinary System Work? Different portions of the tubule selectively
modify the fluid as it travels through them; nutrients are selectively reabsorbed, while wastes remain behind to form urine.• The Bowman’s capsule channels fluid into the
proximal tubule.• The fluid then moves through the loop of
Henle and the distal tubule.• The distal tubules of multiple nephrons drain
into a collecting duct that conducts urine to the ureter.
Copyright © 2009 Pearson Education Inc.
34-35.8 How Does The Human Urinary System Work? Blood is filtered by the glomerulus.
• Urine formation starts with the process of filtration.
• Blood enters each nephron by an arteriole that branches off the renal artery.
• The arteriole branches into capillaries that form the glomerulus.
Copyright © 2009 Pearson Education Inc.
34-35.8 How Does The Human Urinary System Work? Blood is filtered by the glomerulus (continued).• Blood pressure within the capillaries forces
water and dissolved substances through the wall of the glomerulus.
• The resulting watery fluid is called the filtrate.
Copyright © 2009 Pearson Education Inc.
34-35.8 How Does The Human Urinary System Work? The filtrate is converted to urine in the
tubules of the nephron.• This filtrate contains a mixture of wastes,
essential nutrients, and water.• The nephron must restore the nutrients and
most of the water to the blood while retaining the wastes for elimination.
• This process is accomplished by the two processes of tubular reabsorption and tubular secretion.
Copyright © 2009 Pearson Education Inc.
34-35.8 How Does The Human Urinary System Work? Tubular reabsorption moves water and
nutrients from the nephron to the blood.• From Bowman’s capsule, the filtrate passes
through the proximal tubule where most of the water and nutrients in the filtrate move from the proximal tubule into the capillaries; this process is called tubular reabsorption.
• Salts and nutrients are actively transported out of the proximal tubule into the extracellular fluid, and then diffuse into the surrounding capillaries to return to the blood.
Copyright © 2009 Pearson Education Inc.
34-35.8 How Does The Human Urinary System Work? Tubular secretion moves wastes from the
blood into the nephron.• In tubular secretion, wastes such as hydrogen
ions, potassium, ammonia, and many drugs are moved from the capillaries into the nephron.
• Cells of the distal tubule actively transport wastes from the surrounding extracellular space into the tubule, creating a concentration gradient from blood in the capillaries to the extracellular fluid; the wastes thus diffuse out of the capillaries.
Copyright © 2009 Pearson Education Inc.
34-35.8 How Does The Human Urinary System Work? Urine becomes concentrated in the
collecting ducts.• Concentration of urine occurs in the collecting
ducts through the removal of water.• As filtrate travels through the collecting ducts
to the renal pelvis, it passes through areas of increasingly concentrated extracellular fluid.
• Water leaves the filtrate by osmosis and is carried off by the surrounding capillaries.
Copyright © 2009 Pearson Education Inc.
Filtration: Water, nutrients,and wastes are filtered from theglomerular capillaries into theBowman’s capsule of the nephron
Tubular reabsorption: In theproximal tubule, most water and nutrientsare reabsorbed into the blood
Tubular secretion:In the distal tubule,additional wastes areactively secreted into thetubule from the blood
Concentration: Inthe collecting duct,additional water mayleave, creating urinethat is more concentratedthan the blood
34-35.8 How Does The Human Urinary System Work? Urine formation in the nephron and
collecting duct
Fig. 34-35-19
Copyright © 2009 Pearson Education Inc.
34-35.8 How Does The Human Urinary System Work? Negative feedback regulates the water content of
the blood.• The amount of water reabsorbed into the blood is
controlled by negative feedback.• Antidiuretic hormone (ADH) regulates the amount of
water reabsorbed by the collecting ducts.• It does this by increasing the permeability of the distal
tubule and the collecting ducts to water.• The release of ADH from the pituitary is regulated by
receptor cells in the brain that monitor blood concentration.
Copyright © 2009 Pearson Education Inc.
34-35.8 How Does The Human Urinary System Work? Dehydration
stimulates ADH release and water retention.
Fig. 34-35-20
Receptors in the brain detectthe low water content of theblood and signal the pituitarygland
ADH increases thepermeability of the distal tubuleand the collecting duct,allowing more water to bereabsorbed into the blood
Water is retained in the bodyand concentrated urine isproduced
The pituitary glandreleases ADH into thebloodstream
Heat causes waterloss and dehydration
Copyright © 2009 Pearson Education Inc.
34-35.8 How Does The Human Urinary System Work?
PLAYPLAY Animation—Urine Formation