3.4 HOMEOSTASIS IN HUMANS

Necessity of maintaining optimal physics and chemical conditions in the internal environmentIs the extracellular fluid that bathed the cells of

multicellular organismsThe internal physical and chemical environment

must be regulated and maintained at a balanced equilibrium

This is to ensure that the body cells could function efficiently and the physiological processes could proceed at optimum rate

The regulation of physical and chemical factors of internal environment is known as homeostasis whereby a negative feedback mechanism is involved

Internal environment

Physical factors

-Temperature-Blood pressure

Chemical factors

-Partial pressure of oxygen and carbon

dioxide-Osmotic pressure

-Sugar level

Changes in blood osmotic pressure to urine outputThe amount of urine output is actually

related to the amount of water in the blood of the blood osmotic pressure

The more the amount of water in the blood, the lower the blood osmotic pressure

The less the amount of water in the blood, the higher the blood osmotic pressure

Hot shining day Cold rainy day•Our body loses water through sweating•The amount of water in the blood is low, the blood osmotic pressure increase •More water reabsorbed into the blood by the kidneys•The amount of urine eliminated decreases

•Our body not loses water through sweating•The amount of water in the blood is high, the blood osmotic pressure decrease•Less water reabsorbed into the blood by the kidneys•The amount of urine eliminated increases

Structure of the kidneys and their functionThe kidneys are the organ of excretion and

osmoregulationExcretion – is the removal of the metabolites that

have exceeded a critical concentration and the waste products of metabolism out of the body

Osmoregulation – is the control of and the regulation of the volume and composition of body fluid

Situated in the dorsal wall of the abdomenThe tissues in kidney divided into outer cortex

and inner medulla

The excretory unit is tubular unit called nephron and each kidney consist of about one million nephrons

Eevery nephron composed of:I. Bowman’s capsuleII. Proximal convoluted tubuleIII. Loop of HenleIV. Distal convoluted tubuleV. Collecting ductVI. Glomerulus and a network of capillaries

Human excretory system

Formation of urineThe formation of urine involves three

processes:UltrafiltrationReabsorptionsecretion

UltrafiltrationOccurs at glomerulusThe high hydrostatic pressure in the glomerulus

causes many constituents of the blood to be filtered out from the glomerulus into Bowman’s capsule

The filtrate called glomerulur filtrateThe characteristics of glomerulur filtrate:

Has similar composition as the blood plasma except that it does not contain larger components such as RBC and plasma protein

Composed of water, urea, glucose, amino acids, vitamins and salts

The glomerular filtrate then passes along nephon to let reabsorption occur

Reabsorption When the glomerulur filtrate reaches the

proximal convoluted tubule, 65% of the water is reabsorbed to the blood capillaries by osmosis

All glucose, amino acids, vitamins and some salts are reabsorbed by active transport. Urea is not reabsorbed

The filtrate now contains only water, some salts and urea

It continue to pass along the loop of Henle where 20% of the water and some salts are reabsorbed into the blood capillaries

The filtrate continue to pass through the distal convulated tubule and collecting duct whereby some water and salts are reabsorbed into the blood capillaries

The amount of water and salts reabsorbed is actually regulated or controlled by the endocrine system. Ex: amount of ADH and aldosterone

Secretion This process involves the pumping out of the waste

products from the blood capillaries into tubulesNitrogenous products such as urea, uric acids,

ammonia and creatinine are pumped out by active transport

Some drugs and toxic substances are secreted by simple diffusion

The glomerular filtrate that reaches the collecting duct is called urine

It composed of 96% water, 2.5% nitrogenous products and 1.5% salts and other trace elements

Urine is channel out of the collecting duct into pelvis, then out of the kidney into the bladder ureter and finally excreted out of the body through urethra

Osmoregulation Is a process of regulating salts and water

balance in the body to maintain the blood osmotic pressure

The amount of water and salts in the blood determines the blood osmotic pressureThe more the amount of water in the blood,

the lower the blood osmotic pressure The less the amount of water in the blood,

the higher the blood osmotic pressure

Mechanism of osmoregulation

Consequence of impaired kidney functionIf the kidney fail to function as an excretory

organ or as an osmoregulation organ:Metabolic waste cannot be excretedBlood osmotic pressure cannot be regulatedTissue fluid osmotic balance cannot be

maintenedThe patient with kidney failure could be

treated by:HaemodialysisKidney donation or kidney transplant

HaemodialysisIs a process whereby a dialysis machine to

remove metabolic waste such as excess water, urea and excess salts from blood

The producer is expensive, inconvenient and takes long time (6-10 hours and 3 times a week)

How does a dialysis machine work?

Kidney donation and kidney transplantAnother alternative of treating kidneyWith successful transplant, the person may

expert to live for several yearsA suitable kidney donor is needed. A

healthy donor may donate one of his kidney since another healthy kidney could function as an organ osmoregulation

The failed kidney has to be removed from the patient and replaced

What are the major problems persist in this treatment?Immunological rejection- the patient’s

immune system may rejected the grafted kidney

The availability of kidneys- the numbers of patient on the waiting list

Regulation of blood sugar level

Regulation of body temperature

•Must be kept within a certain range for normal metabolic needs•If the pressure is too high, organs may be damaged•If the pressure is too low, organs may not function

Regulation of blood pressure

Concept of homeostasisIs the process where the internal environment is

maintained in spite of the changing environmentTo maintain homeostasis, both the nervous

system and the endocrine system are involved in internal communication

If the communication is by nerve impulses, the effectors that bring about corrective response are the muscles and glands

Is the communication is by hormone, the effectors that bring about corrective response are target organ