Regulatory Role of Kidney

Electrolyte Composition of Body Fluids

• ECF

  • Major cation

  • Major anion

• ICF

  • Chief cation

  • Chief anion

ECF:

• Major cation: Na+

• Major anion: Cl-

ICF:

• Chief cation: K+

• Chief anion: PO4-

How are the kidneys involved in the maintenance of homeostasis of ECF?

Regulates the composition and volume of ECF

Regulation of Water Intake

• Thirst mechanism is triggered by

• Thirst is gone by

  • Results in

Thirst mechanism is triggered by:

• Increase in ECF osmolality

• Decrease plasma volume

Thirst is gone by: Moistened of mucosa of mouth and distention of stomach and intestines

• Results in: Inhibition of hypothalamic thirst center

Influence of ADH

• What is proportional to ADH release

• What occurs when ADH is low

  • Results in

• What occurs when ADH is high

• How is ADH secretion promoted or inhibited

What is proportional to ADH release: Amount of water reabsorbed in collecting ducts

What occurs when ADH is low: Most water in CD is NOT reabsorbed

• Results in: Diluted urine

What occurs when ADH is high: Water in CD is reabsorbed

• Results in: Concentrated urine

How is ADH secretion promoted or inhibited: By the hypothalamus in response to change in

• Solute concentration of ECF

• Changes in blood volume/pressure

Regulation of Plasma Volume of ECF

• ECF volume decreases, what happens to reabsorption of Na and H2O?

• ECF volume increases, what happens to reabsorption of Na and H2O?

• What are the sensors

  • Secrete

  • Leads to

• So when Na decreases, aldosterone

ECF volume decreases, what happens to reabsorption of Na and H2O: Reabsorption increases

ECF volume increases, what happens to reabsorption of Na and H2O: Reabsorption decreases

What are the sensors: Carotid baroreceptors, juxta cells, macula densa

• Secrete: Renin

• Leads to:

  • Increased aldosterone secretion —>

  • Increase Na+ reabsorption —>

  • Increase ECF volume

Na decreases: Aldosterone increases

Osmotic Regulation of ADH

• ADH released from

• ADH release regulated by

• What cells monitor the osmolality of ECF

• Increase in ECF osmolality causes ADH release to

  • Results in

• What is the negative feedback to inhibit additional release of ADH

ADH released from: Posterior pituitary gland

ADH release regulated by: Changes in ECF osmolality

What cells monitor the osmolality of ECF: Osmoreceptors in the hypothalamus

Increase in ECF osmolality causes ADH release to: Increase

• Results in: Excretion of a small volume of hypertonic urine

What is the negative feedback to inhibit additional release of ADH: Reduction in ECF osmolality by excretion of large volume of dilute urine

Regulation of Aldosterone Secretion

• What are the factors that regulation aldosterone secretion

  • How

Blood Volume or Cardiac Output

• How:

  • When blood volume of cardiac output decrease

  • Loss of Na+ and water is compensated by

  • Increase in aldosterone secretion by

  • Adrenal cortex to increase tubular Na+ absorption

Physical Stress

• How:

  • Increase physical stress causes

  • Anterior pituitary gland to increase secretion of ACTH (adrenocorticotrophic hormone)

  • Which stimulates aldosterone secretion by adrenal cortex

Regulation of Water Loss #00a9ff

• Where is ADH synthesised

• Where is ADH stored and released from

• What is the main function of ADH in kidneys

• How does ADH increase water reabsorption

• What cells detect changes in osmolality

• When there’s less water

  • Osmolality is

  • Function of osmoreceptors

  • Results in ADH secretion to

• When there’s excess water

  • Osmolality is

  • Function of osmoreceptors

  • Results in ADH secretion to

Where is ADH synthesised: Hypothalamus

Where is ADH stored and released from: Posterior pituitary gland

What is the main function of ADH in kidneys: Increase water reabsorption in distal tubules and collecting ducts

How does ADH increase water reabsorption: Increases permeability of tubule walls to water

What cells detect changes in osmolality: Osmoreceptors

When there’s less water:

• Osmolality is: Increase

• Function of osmoreceptors: Crenate and stimulate

• Results in ADH secretion to: Increase

When there’s excess water:

• Osmolality is: Decrease

• Function of osmoreceptors: Expand

• Results in ADH secretion to: Inhibited

Polyuria

• What

• How can animals become polyuric

What: The passage of larger volumes of urine than normal

How become polyuric: When animals cannot generate hypertonic urine when necessary

Polydipsia #ff7f00

• What

What: Excessive thirst

How can animals develop polyuria and polydipsia?

Due to unregulated diabetes mellitus (increase blood glucose) because

• Renal tubules cannot reabsorb the abnormally large amounts of glucose in glomerular filtrate

• So the glucose that remains in renal tubules exert osmotic effect to retain water in tubules

• Causing increased urine flow so animal must increase water intake to maintain water balance

How else can polyuria and polydipsia develop?

If ADH is not available or kidney doesn’t respond to ADH which causes

• Water permeability of collecting ducts to decrease

• So water can’t be reabsorbed from collecting ducts into blood

Aldosterone & Potassium Secretion

• What effect does aldosterone have on K

• What happens to K levels in urine when aldosterone increase

• What happens to plasma K conc when aldosterone increase

• How does K reach urine

• What happens if there’s unregulated aldosterone secretion

What effect does aldosterone have on K: Promotes K secretion by principal cells in distal tubules and collecting ducts

What happens to K levels in urine when aldosterone increase: Urinary K loss increases

What happens to plasma K conc when aldosterone increase: It decreases to maintain K balance

How does K reach urine: Through tubular secretion in collecting duct

What happens if there’s unregulated aldosterone secretion: Causes severe plasma potassium loss