Chapter 20 - Urinary System Flashcards Preview

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Flashcards in Chapter 20 - Urinary System Deck (10)
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Describe the location and structural features of the kidneys.
(Learner objective)

The kidneys are located on either side of the vertebral column in depressions on the upper posterior wall of the abdominal cavity.

They are smooth, been shaped organs with a reddish brown colour. Adult kidneys are enclosed into half, fibrous capsules.

Kidneys are about 12 cm long by 6 cm wide and 3 cm thick. Each kidney has a convex lateral surface and a concave medial side resulting in a medial depression.


Describe how antidiuretic hormone and aldosterone influence the volume and concentration of urine.

(Learner objective)

Urine volume and concentration are affected by antidiuretic hormone and aldosterone hormone in differing ways.

Antidiuretic hormone causes distal convoluted tubules and collecting ducts to increase water reabsorption by osmosis. This concentrates during, and volume decreases.

Aldosterone may stimulate additional reabsorption of sodium and secretion of potassium from the distal convoluted tubule.


The urinary system consist of:

2 kidneys
2 Ureters
A Urinary bladder
A Urethra


The urinary system has three major functions

1 excretion: which is the removal of organic waste from body fluids

2 elimination: the discharge of these wastes into the environment

3 homeostatic regulation, of the volume and salute concentration of blood plasma.

The urinary system filter is approximately 200 L of fluid from the bloodstream every day


Other important functions of the kidneys

Secretion of the hormone every erythropoietin, which helps to control red blood cell production.

Helping with the activation of vitamin D

Helping to maintain blood volume and pressure via secretion of the enzyme renin

Carrying out gluconeogenesis while fasting for long periods



The kidneys are positioned behind the parietal peritoneum, against the deep muscles of the back, which is described as retroperitoneally.


Renal sinus


Each kidney has a convex lateral surface and a concave medial side, resulting in a medial depression leading to a hollow ‘renal sinus’.

This Chambers entrance is called the ‘hilum’, through which passed blood vessels, nerves, lymphatic vessels, and the ureter.


Antidiuretic hormone (ADH)

Inhibits urine output, causing the principal collecting duct cells to be more permeable to water, via aquaporin insertion into their apical membranes.

Quantities of ADH determine members of aquaporins and amounts of water reabsorbed there.

Overhydration causes osmolality of extracellular fluid to decrease. This decreases ADH secretion by the posterior pituitary, making the collecting ducts nearly impermeable to water. ADH also increases urea reabsorption by the collecting ducts.



Controls reabsorption of remaining sodium ions.

The adrenal cortex releases aldosterone to the blood because of decreased blood volume or pressure, or hyperkalaemia.

Decreased blood volume or pressure promote the renin-angiotensin-aldosterone mechanism.

Hyperkalaemia directly stimulates the adrenal cortex to secrete aldosterone.

Aldosterone enhances sodium reabsorption, helping to increase blood volume, and then blood pressure.

When aquaporins are present, water usually follows sodium. Aldosterone also reduces blood potassium because it’s reabsorption of sodium is coupled with potassium secretion in the principal collecting duct cells. As sodium enters the cells, potassium moves into the lumen.


Antidiuretic hormone (ADH) and urine

Plasma volume - concentration of water decreases

Body fluids - increase in osmotic pressure stimulates osmoreceptors in the hypothalamus

Hypothalamus - signals posterior pituitary to release ADH

Blood - carries ADH to kidneys

ADH - causes distal convoluted tubules and collecting ducts to increase water reabsorption by osmosis

Urine - becomes concentrated, and urine volume decreases