physiology : excretion

Principles of physiology

Nutrition, Digestion & Metabolism

Blood

Respiration

Excretion

Muscular system

Nervous system

Endocrine system

EXCRETION

LUNG

Excrete carbondioxide and water

The wastes of cellularrespiration

Removes

toxic substancesfrom the blood

Converts

hemoglobin fromold RBC’s to bilepigments

eliminated in thefeces

LIVER

Disposal of nitrogenous wastes

Breaks down excess

amino acids (deamination)

Amino group ammonia urea

Urea transported to the kidneys by the blood

Skin sweatglands

excretostructurof the s

URINARY SYSTEM

kidneys,

ureters,

urinary

bladder

urethra

URINARY SYSTEM

kidneys (2) are beanshaped organs ,10 cm long ,located below thediaphragm nearthe back

3 main functions:

1. Excretion(remove wastes of cellularmetabolism from the blood)

2. Regulation, homeostasis(concentrations of substances found inbody fluids,plasma,pH, blood pressure)

3. Secretion (rennin, and erythropoietin)

Kidney Structure

Kidneys consist ofmicroscopic

structures called

NEPHRONS.

A NEPHRONMade of :1- Glomerulus: a network ofcapillaries

2- Bowman’s

capsule:

cup-like structuresurrounding theglomerulus

3- Renal tubule

Proximal convolutedtubule (PCT)

longest, most coiled,simple cuboidal withbrush border

Nephron loop - Ushaped; descending +ascending limbs

Distal convoluted tubule(DCT)

cuboidal, minimalmicrovilli

Juxta-glomerular apparatus:

A group of spindle shaped cells in the mediaof afferent glomerular arterioles

-Secrete rennin ( increase renal blood flow ). -Secrete erythropoietine, a hormonal agentnecessary for production of red blood cellsby bone marrow.

-Secrete chemical factor ,regulate the outputof aldosterone.

A nephron works in 3 stages: 1- Filtrations stage: water, minerals,

salts, urea, amino acids and glucose arefiltered out of the blood

Filterate170-180L/dayresemble blood plasma (except RBCs,plasma

protein

3 forces : High glomerular capillaries pressure

High glomerular osmotic pressure

Low filterate pressure

2- Reabsorptionstage:

water, minerals,amino acids and

glucose arereabsorbed byactive transportfrom the renaltubule into thecapillaries

3- Secretion stage

Urine Formation Preview

Urine Volume

Normal volume - 1 to 2 L/day

Polyuria > 2 L/day

Oliguria < 500 mL/day

Anuria - 0 to 100 mL

DiabetesChronic polyuria

With hyperglycemia and glycosuria

diabetes mellitus I and II, insulinhyposecretion/insensitivity

gestational diabetes, 1 to 3% of pregnancies pituitary diabetes, hypersecretion of GH adrenal diabetes, hypersecretion of cortisol

With glycosuria but no hyperglycemia renal diabetes, hereditary deficiency of glucose

transporters

With no hyperglycemia or glycosuria

diabetes insipidus, ADH hyposecretion

URETERS

Tubes

carry urinefrom thekidney to thebladder

URINARY BLADDER

Stores urine

URETHRA

Tube thatcarries urinefrom thebladder to theoutside of thebody

Function - Homeostasis

Acid-Base Balance Kidneys regulate the pH, mineral ion concentration,and water composition of the blood.

By exchanging hydronium ions and hydroxyl ions,the blood plasma is maintained by the kidney at pH

7.4. Urine, becomes either acidic at pH 5 or alkaline atpH 8.

Water Balance Aldosterone

Plasma Volume ADH

Aldosterone

A steroid hormone (m alocorticoid)

It is formed in the outer-section (zona

glomerulosa) of the adrenal cortex

It diminishes the excretion of Na+ ions andtherefore water, and stimulates the excretionof K+ ions by the kidneys.

ADH (VASOPRESSIN) when the body is low on water.

kidneys conserve water

osmotic activity increase

con. urine.

→ stimulate OSMOTIC RECEPTORS in thehypothalamus

→ stimulation of posterior pituitary lobe

→ activation of VASOPRESSIN→ increase collecting ducts permeability for water

→ reabsorption →HYPERTONIC URINE

Malfunctions

Kidney Diseases: Various conditions in which thekidneys are unable to properlyexcrete nitrogenous wastes

Kidney stones: Substances crystalize out of the urinein the urinary tract or in the kidney

Some pass out in the urine on theirown

Some can be shattered with lasers orsound waves

Some are surgically removed

Dialysis - cansome times be usedto treat variouskidney diseases

Kidneytransplants