Chapter 37

Maintaining the Internal Environment

37.1 How Do Animals Maintain the Composition of Their Body Fluids?

• By weight, an animal consists mostly of water with many dissolved salts and other solutes

• Major aspect of homeostasis involves keeping the solute composition and volume of the extracellular fluid within a normal range– Water and solute gains need to be balanced

by water and solute losses

How Do Animals Maintain the Composition of Their Body Fluids?

• Metabolic reactions alter the composition of extracellular fluid– Example: breakdown of proteins produces

ammonia• Most animals have organs that rid their body of

waste ammonia and other unwanted solutes

Organs That Adjust Body Fluids (cont’d.)

• All vertebrates have a pair of kidneys: organs that filter the blood, adjust its composition, and produce urine– Urine: consists of water and soluble wastes

37.2 Structure of the Urinary System

• Human kidneys are bean-shaped organs about the size of an adult fist

• They lie just inside the peritoneum that lines the abdominal cavity

• The outermost kidney layer, the renal capsule, consists of fibrous connective tissue

Introducing Nephrons

• Nephrons: kidney tubule and associated capillaries; filters blood and forms urine

• Bowman’s capsule: forms cup around the glomerulus; connects to proximal tubule

• Proximal tubule: tubule nearest Bowman’s capsule

Concentrating the Urine

• Water moves out of a nephron by osmosis– A high solute concentration in interstitial fluid

draws water out of filtrate as it flows through the descending loop of Henle

– As urine descends through the collecting tubule, the increasing solute concentration of the interstitial fluid around the tubule draws water outward by osmosis

37.4 What Causes Kidney Problems?

• The vast majority of kidney problems arise as complications of diabetes mellitus or high blood pressure– These disorders damage the capillaries that

interact with nephrons

• Kidney dialysis removes wastes and restores proper solute concentrations in a person who has kidney failure

37.5 What Can Urine Tests Detect?

• Physicians routinely check the pH and solute concentrations of urine to monitor their patients’ health– Acidic urine: metabolic problems– Alkaline urine: infection– Sugar in the urine: diabetes– Urine high in proteins: damaged kidneys– High salt in urine: dehydration; hormone

deficiencies

37.6 How Do Animals Regulate Body Temperature?

• Thermoregulation: maintaining body temperature within a limited range– Important because enzymes work best within

a limited range of temperatures

Vertebrate Responses to Cold (cont’d.)

• Skeletal muscles are a vertebrate’s main source of metabolic heat– With prolonged exposure to cold, the

hypothalamus commands these muscles to contract ten to twenty times each second

– Shivering response increases metabolic heat production

Vertebrate Responses to Heat

• In a hot environment, a vertebrate becomes less active– Decreases the amount of heat produced by

the activity of its skeletal muscles

• Blood delivery to the skin increases, allowing more metabolic heat to escape into the surroundings

Vertebrate Responses to Heat (cont’d.)

• Many vertebrates reduce their temperature by breathing rapidly (panting)– Increases the rate of evaporative cooling from

the respiratory system

• Sweating is the main mechanism of cooling in primates (including humans) and large hooved mammals

• Rodents and marsupials cool off by spreading saliva on their skin

37.7 How Do Humans Respond to Heat and Cold?

• A negative feedback mechanism maintains the human core body temperature at about 98.6° Fahrenheit (37°C)

• When our core temperature rises above this point, blood flow to our skin increases and we begin to sweat

• In a cold environment, humans warm themselves by shivering and, in some cases, by nonshivering heat production

Chapter 38

Reproduction and Development

38.1 How Does Animal Reproduction Vary?

• Asexual reproduction– Offspring are genetic replicas (clones) of the

parent and identical to one another– Mechanisms include:

• Budding• Fragmentation• Transverse fission• Parthenogenesis

How Does Animal Reproduction Vary?

• Sexual reproduction– Two parents produce haploid gametes (eggs

and sperm) that combine at fertilization– Each offspring has a unique combination of

paternal and maternal genes– Advantageous when the environment

changes over time

How Does Animal Reproduction Vary?

• Gamete formation and fertilization– Hermaphrodites are sexual reproducers that

produce both eggs and sperm• Simultaneous hermaphrodites• Sequential hermaphrodites

How Does Animal Reproduction Vary?

• External fertilization – Sperm and egg are released into the external

environment and meet there– Animals that reproduce in water have external

fertilization

• Internal fertilization– A female retains eggs in her body and sperm

fertilize them there– Land animals use internal fertilization

38.6 What Are Functions of a Man’s Reproductive Organs?

• Male reproductive anatomy– A human male’s gonads are paired testes

• Produce sperm • Secrete the male sex hormone testosterone

– Epididymis• Coiled duct where sperm mature and are stored

– Vas deferens• A series of ducts convey sperm from testes to the

body surface

What Are Functions of a Man’s Reproductive Organs?

• Penis– Male organ of intercourse– Also functions in urination– In sexual excitement, three elongated

cylinders of spongy tissue in the penis fill with blood and cause an erection

What Are Functions of a Man’s Reproductive Organs?

• Semen– Secretions of exocrine glands that empty into

the male reproductive ducts – Join with sperm– Seminal vesicles secrete fructose-rich fluid

used by sperm as an energy source; the prostate contributes to semen volume; and bulbourethral glands secrete a lubricating mucus

38.7 What Are Functions of a Woman’s Reproductive Organs?

• Female reproductive anatomy– A human female’s gonads are paired ovaries

• Lie deep inside the pelvic cavity• Produces and releases immature eggs (oocytes)• Secretes estrogens and progesterone, the main

sex hormones of females

What Are Functions of a Woman’s Reproductive Organs?

• Lowest portion of the uterus, a narrowed region (cervix) opens into the vagina– Female organ of intercourse and birth canal

• When a woman becomes pregnant, the embryo attaches to the uterine lining (endometrium) and completes its development inside the uterus

What Are Functions of a Woman’s Reproductive Organs? (cont’d.)

• Oocyte maturation and release– Female germ cells do not divide after birth– A girl is born with about 2 million primary

oocytes (immature eggs suspended in prophase I of meiosis) in her ovaries

– At puberty, hormonal changes prompt primary oocytes to mature, one at a time, in an ovarian cycle (about 28-days)

38.8 How Do Hormones Affect the Female Reproductive Cycle?

• Menstrual cycle – Approximately 28-day cycle– Uterus lining thickens and then, if pregnancy

does not occur, is shed– Hormones coordinate cyclic changes in

ovaries and uterus– Menstruation

• Flow of shed uterine tissue out of the vagina

38.9 How Does Human Fertilization Occur?

• Egg and sperm may meet as a result of sexual intercourse

• For males, intercourse requires an erection – aging, circulatory problems, and smoking affect erectile function

• When a woman becomes sexually excited, glands in the cervix secret mucus, and glands on the labia produce a lubricating fluid

How Does Human Fertilization Occur? (cont’d.)

• Fertilization– Ejaculation puts about 300 million sperm (live

for about three days) into the vagina– Sperm swim upward into the oviduct, where

fertilization of a secondary oocyte, released at ovulation, usually occurs

How Does Human Fertilization Occur? (cont’d.)

• Fertilization (cont’d.)– The secondary oocyte is covered with follicle

cells over a layer of secreted proteins that form a jelly coat around it

– The plasma membrane of the sperm’s head has receptors that bind species-specific proteins in the jelly

How Does Human Fertilization Occur? (cont’d.)

• Fertilization (cont’d.)– Binding of sperm to egg proteins triggers the

release of protein-digesting enzymes from the cap on the sperm’s head

– Receptors in oocyte’s plasma membrane bind a sperm’s plasma membrane, the two membranes fuse, and the sperm enters the secondary oocyte

– The egg’s jelly coat changes to prevent other sperm from binding

How Do People Avoid Pregnancy? (cont’d.)

38.11 What Are Sexually Transmitted Diseases?

• Each year, pathogens that cause sexually transmitted diseases (STDs) infect about 15 million Americans

• Women are more easily infected than men, have more complications, and can pass an STD on to her newborn

• Both men and women can be debilitated by body-wide effects of some infections

What Are Sexually Transmitted Diseases?

• The most common bacterial STD is now chlamydia (Chlamydia trachomatis), which often causes no symptoms in women, but can infect her child– Bacteria also cause gonorrhea (infect

oviducts, causing cramps, scarring, and sterility in women), and syphilis (damages liver, bones, and eventually the brain)

• Bacterial STDs can be cured with antibiotics

What Are Sexually Transmitted Diseases? (cont’d.)

• HPV infection is widespread in the United States (about 100 HPV strains)– A few strains cause genital warts– Some strains of HPV cause cervical cancer

• Sexually active females should have an annual Pap smear to screen for signs of cancer

• Viral diseases cannot be cured by drugs– A vaccine (Gardasil) can prevent some types

of HPV infection if given before viral exposure

What Are Sexually Transmitted Diseases? (cont’d.)

38.14 What Is the Role of the Human Placenta?

• All exchange of materials between an embryo and its mother takes place across the placenta

• A placenta is a pancake shaped, blood-engorged organ made of uterine lining and extraembryonic membranes

• The embryo/fetus is connected to the placenta by an umbilical cord

What Is the Role of the Human Placenta? (cont’d.)

• The placenta– Forms early in pregnancy

• By third week, chorionic villi are growing into pools of maternal blood in endometrial tissue

– Maternal and embryonic bloodstreams never mix

– Oxygen and nutrients diffuse from maternal blood into embryonic blood

– Wastes diffuse the other way, and the mother’s body disposes of them

What Is the Role of the Human Placenta? (cont’d.)

• Vitamin and mineral deficiencies affect development– Folate and iodine deficiency

• Viruses can pass from mother to her embryo or fetus– Example: Rubella (German measles)

• Many toxins can cross the placenta– Alcohol, caffeine, drugs, medications, tobacco

smoke

38.15 How Is a Child Born and Nourished?

• Shifts in hormone levels control birth (labor) and milk production (lactation) – Labor

• Expulsion of a placental mammal from its mother’s uterus by muscle contractions

– Lactation • Milk production by a female mammal

What Is the Role of the Human Placenta? (cont’d.)

• Lactation (cont’d.)– Besides being nutrient-rich, human breast

milk has antibodies that protect a newborn from some viruses and bacteria

– Nursing mothers should keep in mind that drugs, alcohol, and other toxins also can end up in milk

38.16 Reproductive Technology

• In vitro fertilization (IVF)– Reproductive technology which combines egg

and sperm outside the body• A woman can use donated eggs and IVF to

produce blastocysts that she carries to term• A woman with fertile eggs can have a blastocyst

conceived by IVF implanted in a surrogate mother

– Prospective parents can screen blastocysts produced by IVF to avoid genetic defects, or choose desirable traits

Using appropriate information, fill in spaces A and B in the chart below. In space A identify an organ in the human body where molecules diffuse into the blood. In space B identify a specific molecule that diffuses into the blood at this organ.

HOMEOSTASIS

• How does circulation maintain homeostasis?• How does the excretory system maintain

homeostasis?• How does the respiratory system maintain

homeostasis?