9.0 HOMEOSTASIS

BY : MDM. NURFAZLINI ISMAIL

9.1 CONCEPT OF HOMEOSTASIS

• Explain the concept of homeostasis and describe the homeostatic control system

• Homeostasis is the process of maintaining biologically stable condition inside a living organism / body (through physiological processes)

• Involves many regulatory process

• Any disruption that changes a controlled condition is called a stimulus

Basic components of a

feedback system• Body structure that monitors changes in a

controlled condition and sends input in the

form of nerve impulses or chemical signals to

a control center.

• Sets the range of values within which a

controlled condition should be

maintained, evaluates the input it

receives from receptors and generates

output commands when they are

needed.

Basic components of a

feedback system

• Output from the control center can

occur in forms of nerve impulses,

hormones or other chemical signals

• Muscles or glands that receives output

from the control centre and produces a

response or effect that changes the

controlled condition.

Basic components of a

feedback system

• The effector response by either

depressing it (negative feedback) or

enhancing it (positive feedback)

Set point

(optimal level)

Set point

(optimal level)

excess

deficiency

correction

mechanism

correction

mechanism

negative

feedback

negative

feedback

positive

feedback

positive

feedback

Further excess

Further deficiency

Feedback Mechanism

Feedback Mechanism:Negative Feedback• A mechanism that stops or reduces

the intensity of the original stimulus

• and consequently causes a change in a variable that is opposite in direction to the initial change

• The output is used to reduce input.

• A change from the usual level of a factor (the set point for the factor) triggers a corrective mechanism which restores the factor to its usual level.

• Eg. Regulation of Blood Glucose

Feedback Mechanism:Positive Feedback

• Feedback mechanism in which the response enhances the original stimulus

• The output is used to enhance the input

• Example: regulation of blood clotting

9.2 NEGATIVE FEEDBACK MECHANISM

• Explain the negative feedback mechanism in controlling blood glucose

• The brain cells are especially sensitive to glucose and are unable to utilize any other metabolites as an energy sources

• Lack of glucose results in fainting

• The normal level of glucose in the blood is about 90 mg /100 mL blood

• If the level drops below this point, respiration will slow or even stop inducing coma.

• If level becomes too high it has an equally harmful effect.

• A rise in blood glucose level (hyperglycaemia)

• stimulates insulin secretion

• A fall in blood glucose level (hypoglycaemia)

• inhibits insulin secretion

• and stimulates the secretion of glucagon and other hormones( glucocorticoids, adrenaline, growth hormone and thyroxine) which raise blood glucose levels (hyperglycaemic factors)

• There are 3 main sources of glucose :

• Conversion of protein into glucose (gluconeogenesis).

• Conversion of glycogen to glucose (glycogenolysis).

• Carbohydrate including glucose in the diet.

The Pancrease

• The pancreas play a vital role in the regulation of blood glucose level.

• The pancreas has bundle of secretory cell distributed between other cell called Islet of Langerhans.

• 2 type of secretory cells :

• Alfa cell

• Beta cell

• These produce different hormone and monitor blood glucose level.

• Hormone travel to all part of the body via the blood.

• The target cell (liver and skeletal muscle cell).

• Two type of hormones:

i) Insulin

• Produce by beta cell in the islet of Langerhans

• When the glucose level are too high, glycogenesis occurs

• Glucose glycogen

HOMEOSTASIS/FAZ/1718

insulin

ii) Glucagon

• Produce by alfa cells in islet of Langerhans

• When glucose level are too low, glycogenolysis occurs

• Glycogen glucose

HOMEOSTASIS/FAZ/1718

glucagon

Negative Feedback:Controlling blood glucose level

• Blood glucose level is regulated by islets of Langerhans in the pancreas

• These cells act as sensor and integration center

• When blood glucose concentration is high / hyperglycemia

• β cells secretes insulin

• Insulin stimulates uptake of glucose from the blood

• By muscle cells / liver / adipose tissue

• Glycogen is converted to glycogen in muscle cells and liver

• Glycogen is store in the liver

HOMEOSTASIS/FAZ/1718

• These tissue act as effector

• Insulin inhibits liver cells from releasing glucose

• When blood glucose liver is low // hypoglycemia

• α cells secretes glucagon

• Converts other metabolites to glucose // gluconeogenesis

• Fatty acid and amino acid are converted to glucose

• Involves negative feedback mechanism

HOMEOSTASIS/FAZ/1718

9.3 HUMAN HOMEOSTATIC ORGAN : KIDNEY(STRUCTURE AND FUNCTIONS OF KIDNEY)• Describe the structure of nephron

Renal artery

Urinary bladder

Ureter

Urethra

KidneyRenal vein

Mammalian Excretory System

Kidney structureSection of kidneyfrom a rat 4 mm

Renalcortex

Renalmedulla

Renalpelvis

Ureter

The mammalian kidney

has two distinct regions:

an outer renal cortex

and an inner renal

medulla

Structure of Kidney:Cortex• Outer region

• Consist mainly of Malphigianbody (renal corpuscle) and convoluted tubules

• Each renal corpuscle is made up of a network of blood capillaries (glomerulus) enclosed by the Bowman’s capsule (renal capsule)

• Ultrafiltration takes place in renal capsule

Structure of Kidney:Medulla• Middle region

• Contain the Loop of Henle and the collecting ducts.

• Is grouped into structure called renal pyramid

• Collecting ducts group together and send projection into the hollow pelvic region.

Structure of Kidney:Pelvis• Inner region

• An open space which funnels the filtrate (urine) into the ureter.

• Is the functional unit of kidney

• Functions:

• Regulate the composition of body fluids by three main processes

• Glomerular ultrafiltration

• Selective tubular reabsorption

• Tubular secretion

Structure of Kidney:Nephron

• In the cortex close to the junction with the medulla

• Long loop of Henle that extend deep into the medulla

• Important Function when water is in short supply

Types of Nephron:Juxtamedullarynephron

Corticalnephron

Juxtamedullarynephron

Collecting

duct

Nephron types

Torenalpelvis

Renalmedulla

Renalcortex

• Occurs largely in the cortex

• Have short loop of Henle, just reaching the medulla

• Important when water supply is normal to excessive

Types of Nephron:Cortical nephron

Corticalnephron

Juxtamedullarynephron

Collecting

duct

Nephron types

Torenalpelvis

Renalmedulla

Renalcortex

Parts of Nephron:Bowman’s capsule• Located at the closed end of the

tube where the wall of the nephron is pushed in forming a two walled compartment

• Contain glomerulus

• Capillary network enclosed within Bowman’s capsule.

• Renal corpuscle (Bowman’s capsule + glomerulus)

Parts of Nephron:Proximal convoluted tubule• Highly coiled and lined with

cells with microvilli and filled with many mitochondria

• Conducts the filtrate from Bowman’s capsule.

Parts of Nephron:loop of Henle

• Hair-pin shaped

• Have descending limb & ascending limb.

• Located in the medulla of the kidney.

Parts of Nephron:Distal convoluted tubule

• Located in the cortex of the kidney.

• Conducts the filtrate to a collecting duct.

Parts of Nephron:Collecting duct

• End of kidney, located in the medulla of the kidney.

• The collecting ducts all eventually drain into the pelvis of the kidney, from where the urine flows into the ureter.

• Blood enters the kidney by the renal artery from aorta

• Supplies both oxygenated

• branches into afferent arteriole.

Nephron & associated blood vessels:Renal artery

• Blood leaves the kidney through the renal vein to inferior vena cava

Nephron & associated blood vessels:Renal vein

• Brings blood towards each hollow capsule called Bowman’s capsule via glomerulus.

• Dividing to form a network of capillaries (glomerulus)

Nephron & associated blood vessels:Afferent arteriole

• Blood leaves the Bowman’s capsule (glomerulus) in an efferent arteriole

• Narrower than afferent arteriole

• Branch to form vasa recta around nephron before forming venules

• Divided to form capillaries whichsurround the proximal and distalconvoluted tubules and theloops of Henle in the medulla

Nephron & associated blood vessels:Efferent arteriole

• The capillaries of the vasa recta (peritubular capillaries) run parallel to the:• loops of Henle • collecting duct in the

medulla.

Nephron & associated blood vessels:Vasa recta

Renal artery Afferent arteriole Glomerulus

Efferent arterioleVasa rectaRenal vein

Blood Circulation In The Nephron