Renal System

Macroscopic

Adrenal glands

Aorta

Calyx

Glomerular filtrate

Inferior vena cava

Malpighian body

Peristalsis

Prostate gland

Renal artery

Renal cortex

Renal medulla

Renal pelvis

Renal vein

Papilla

Pyramids

Renal capsule

Selective reabsorption

Sphincter

Ultrafiltration

Ureter

Urethra

Urinary bladder

Urine

Microscopic

Afferent arteriole

Antidiuretic hormone

Bowmans capsule

Collecting duct or tubule

Diuretic

Distal (2nd) convoluted tubule

Efferent arteriole

Glomerulus

Loop of Henle, (ascending and descending loop)

Nephron

Proximal (1st) convoluted tubule

Venule

Renal functions

Homeostasis - Acid base balance

Blood pressure

Excretes - Urea Toxins Water

Regulates - Fluid and electrolyte balance

Produces - Renin

- Erythropoietin

Converts - Vit D

Renal system physiology

Blood is filtered under pressure in the kidneys to produce urine.

The cleaned blood is returned to the circulation.

Once formed the urine is propelled down the ureters by peristalsis. These are narrow tubes about 25 cm long with muscular elastic walls.

The ureters empty urine in the bladder. Once urine has passed into the bladder it is not allowed to return into the ureter, this valve mechanism prevents ascending infection.

The bladder lies below the pubic bones low in the pelvis.

The bladder stores urine and is a muscular bag to facilitate the bolus expulsion of the urine from the body.

Urine leaves the body via the urethra, in women this is about 4 cm long, but in men it is about 20 cm.

The neck of the bladder is surrounded by muscles which act as a sphincter to regulate the passage of urine from the bladder.

Micturition occurs when the sphincter relaxes and the muscular bladder wall contracts.

The bladder can easily contain 400 - 600 mls of urine but we usually empty it at about 200 mls.

In women the sphincter is not as well formed as in men and continence is maintained by local muscles and by the contraction of the muscles of the pelvic floor.

Pelvic floor muscles form the bottom of the pelvis and retain the pelvic organs. They are arranged in a front to back direction.

The urethra and vagina pass through the front of the pelvic floor with the rectum to the back.

As women age the pelvic floor muscle tone reduces, this is made worse by childbirth, chronic constipation with resultant straining, any form of trauma and obesity.

The nephron

Ultrafiltration - Selective Absorption - Secretion

Formation of Glomerular Filtrate (Flux)

Capillary hydrostatic pressure 55 mm Hg. (+)

Osmotic pressure of blood 30 mm Hg. (-)

Filtrate hydrostatic pressure 15 mm Hg. (-)

Net filtration pressure

Up to 10,000 pass easily greater difficulty up to 200,000

Plasma flow = 650 mls/min

Rate of formation = 120 mls/min

Selective Reabsorption

Parathormone and calcitonin - regulate absorption of calcium and phospate

Antidiuretic hormone - water reabsorption

Aldosterone - sodium and potassium

Normal specific gravity 1020 - 1030

Tubular secretion

Normal urine contents

Water 96%

Urea 2%

Uric Acid )

Creatinine )

Ammonia )

Sodium )

Potassium ) 2%

Chlorides )

Phosphates )

Sulphates )

Oxalates )

Obligatory urine volume

Normal Glomerular filtrate contains all of the above and ;

water, hormones, vitamins, enzymes, glucose, proteins, amino acids and inorganic salts eg. sodium and calcium

Water balance

In Out

Water 1.5 litres Lungs 0.5

Food 1 Skin 0.5

Metabolic 0.5 Skin 0.5

Sweat variable, up to 3 litres

Urine 1.5

Faeces 0.1

Loss increased in pyrexia and some environmental conditions

Antidiuretic hormone

ADH increases permeability of distal convoluted tubules

ADH increases the reabsorption of water

ADH lowers urine volumes

Osmoreceptors in hypothalamus detect rise in osmotic pressure

Hypothalamus stimulates posterior lobe of pituitary gland to release ADH

By increasing reabsorption ADH conserves water therefore prevents more water loss therefore prevents continued rise in blood osmolarity

.

If water levels rise, ie blood osmotic pressure falls

detected in hypothalamus --------- reduced stimulation of PLPG ------ decreased ADH secretion --------- reduced reabsorption from nephrons ------------- increased urine volumes ---------- reduced amount of water in the blood, ie osmotic pressure rises

If water levels fall, ie blood osmotic pressure rises

detected in hypothalamus------------- increased stimulation of PLPG ------------ increased ADH secretion -------------- increased reabsorption from nephrons ---------- reduced urine volumes ------------ water in blood conserved ie. osmotic pressures prevented from further rise

Endocrine functions

Erythropoietin - Released in response to hypoxia or anaemia

- Stimulates increased red cell production by bone marrow

Renin - Released in response to reduced renal perfusion

converts angiotensinogen to angiotensin ------ vasoconstriction

acts on adrenal cortex --------- increased release of aldosterone ------------- increased reabsorption of sodium and water --------- increased blood volume

Dihydroxycholecalciferol - the active metabolite of Vit. D

Acid base balance

The pH scale

Blood pH 7.4

Blood is an effective buffer

An acid is produced by Hydrogen (H⁺) ions in water

The kidney can secrete H⁺ ions in urine, selectively.

The kidney can secrete or retain bicarbonate (HCO₃^-) ions,