Urine Production and Fluid balance

Excretion - how is urine produced?

- removing all contents
- Put back the useful components
- Get ride of waste products = urine

What happens in the nephrons?

- Function unit of the kidney
- Millions present in each kidney
- Responsible for the filtration of blood and production of urine

What is the first component of a nephron?

Bowman's capsule

What is the second component of a nephron?

Glomerulus

What is the third component of a nephron?

Proximal convoluted tubule

What is the fourth component of a nephron?

Loop of Henle

What is the fifth component of a nephron?

Distal convoluted tubule

What is the sixth component of a nephron?

Collecting duct

Nephrons consist of..

- Bowman's capsule (cortex)
- Glomerulus (cortex)
- Proximal convoluted tubule (cortex)
- Loop of Henle (medulla) into renal pyramids
- Distal convoluted tubule (cortex)
- Collecting duct (medulla) towards the hilum/pelvis

What makes up the renal corpuscle in nephrons?

Bowmans capsule & Glomerulus

Where is the glomerulus located?

Sits within the Bowmans Capsule

What is the function of Bowman's capsule?

Bowman's capsule collects fluid and small molecules that are forced out of the blood during ultrafiltration.

What is the role of the glomerulus in the kidney?

The glomerulus is a dense ball of capillaries where blood is filtered under high pressure.

How does blood pressure in the glomerulus compare to other parts of the circulatory system?

Blood pressure is high in the glomerulus due to the direct supply from the renal artery, which stems from the aorta.

What is ultrafiltration in the context of the kidneys?

Ultrafiltration is the process where high blood pressure in the glomerulus forces fluid and small molecules into Bowman's capsule, while larger molecules like red blood cells remain in the bloodstream.

What is glomerular filtrate?

Glomerular filtrate is the solution produced from the fluid and small molecules that pass into Bowman's capsule during ultrafiltration.

Blood pressure in the glomerulus

Blood pressure rises in the glomerulus because the efferent arteriole has a smaller diameter than the afferent arteriole, creating resistance.

What is the function of the glomerulus in the kidney?

The glomerulus is a dense ball of capillaries where blood is filtered.

How does blood enter the kidney?

Blood enters the kidney via the renal artery.

What causes high blood pressure in the glomerulus?

High blood pressure in the glomerulus is due to blood coming directly from the aorta.

What are the names of the two arterioles associated with the glomerulus?

The two arterioles are the afferent arteriole (incoming) and the efferent arteriole (outgoing).

Why does blood pressure rise in the glomerulus?

Blood pressure rises in the glomerulus because the efferent arteriole has a smaller diameter than the afferent arteriole.

What happens to small components of blood in the glomerulus?

Small components of blood are forced out into Bowman's capsule due to high pressure.

What is the process called when fluid and small molecules are forced out of the bloodstream into Bowman's capsule?

Ultrafiltration

What remains in the bloodstream during ultrafiltration?

Larger molecules such as RBCs (Red Blood Cells)

What is the solution produced from ultrafiltration called?

Filtrate

What is the role of Bowman's capsule in the filtration process?

It collects fluid and small molecules forced out of the blood.

What is the Proximal Convoluted Tubule (PCT)?

The nearest winding tube (convoluted) in the nephron.

What percentage of resorption occurs in the Proximal Convoluted Tubule?

Approximately 65% of all resorption.

Where does the glomerular filate pass onto after the bowman's capsule?

Proximal Convoluted Tubule

What ions are actively reabsorbed from the filtrate in the Proximal Convoluted Tubule?

80% of Sodium (Na) and Chloride (Cl) ions.

What happens in response to Na and Cl reabsorption in the PCT?

Water moves back into the blood supply via osmosis

How does water move back into the blood supply in the Proximal Convoluted Tubule?

By osmosis.

What happens to glucose in the Proximal Convoluted Tubule?

All glucose within the glomerular filtrate is reabsorbed into the blood supply.

In a healthy animal, what will happen to the glucose within the filtrate?

The glucose will be reabsorbed back into the blood supply in the PCT

What does the removal of water do in the PCT?

Concentrates the levels of urea

What type of drugs are actively secreted into the filtrate at the Proximal Convoluted Tubule?

Drugs of the penicillin family.

Why is the Proximal Convoluted Tubule important for penicillin?

It is a useful antibiotic for infections of the urinary tract.

What is the function of the Loop of Henle?

The Loop of Henle regulates the concentration and volume of filtrate.

What is the permeability characteristic of the descending limb of the Loop of Henle?

The descending limb is permeable to water.

What happens to water in the descending limb of the Loop of Henle?

Water is drawn out of the tubule via osmosis due to the high concentration of Na ions in the surrounding peritubular fluid.

What happens to the fluid surrounding the loop of Henle?

Highly concentrated in Na ions therefore water is drawn out of the tubule via osmosis

What is the fluid surrounding the loop of Henle called?

Peritubular fluid, or the surrounding capillaries - known as the Vasa Recta

What occurs to the concentration of filtrate as it moves down the descending limb of the Loop of Henle?

The filtrate becomes more concentrated, reaching maximum concentration at the loop turn.

What is the term for the capillaries that surround the Loop of Henle?

Vasa Recta.

What is the permeability of the ascending limb of the Loop of Henle?

The ascending limb is impermeable to water.

What ions are actively reabsorbed in the ascending limb of the Loop of Henle?

Sodium (Na) ions are actively reabsorbed back into the the peritubular fluid and blood supply

What effect does the active transport of sodium in the ascending limb have on the filtrate concentration?

The filtrate becomes less concentrated as sodium is removed.

How does the concentration of the filtrate change as it ascends the Loop of Henle?

The concentration remains the same as when it entered the loop

What happens to the volume of the filtrate as it moves through the ascending limb of the Loop of Henle?

The volume decreases due to the removal of water

What is the function of the Distal Convoluted Tubule (DCT)?

The DCT is where final adjustments to the filtrate are made, including reabsorption of sodium and secretion of potassium.

What factors influence the function of the Distal Convoluted Tubule (DCT)?

The function of the DCT depends on the health of the animal and the status of the extracellular fluid.

How does the Distal Convoluted Tubule (DCT) help regulate blood pH?

If blood pH is low (acidic), the DCT excretes hydrogen (H+) ions; if pH is high (alkaline), it retains H+ ions.

What is the normal blood pH?

The normal blood pH is 7.4.

What additional substances can be secreted into the filtrate at the Distal Convoluted Tubule (DCT)?

Certain drugs can also be secreted into the filtrate at the DCT.

Where is the Distal Convoluted Tubule (DCT) located in relation to other parts of the nephron?

The DCT is the furthest part away from the renal corpuscle.

distal convoluted tubule

Further reabsorption of Na occurs here but in smaller quantities than previously in the PCT.

What is the final stage in urine production?

The collecting ducts

What can occur in the collecting regarding osmosis?

Water may be drawn out of the ducts via osmosis due to the presence of high Na concentration in the tissue surrounding the collecting ducts

What determines the amount of water drawn out of the collecting ducts?

The hydration status of the animal

What is the filtrate referred to after it enters the collecting ducts?

Urine

Where do the collecting ducts carry urine?

To the renal pelvis

What connects the renal pelvis to the bladder?

The ureter

What can be reabsorbed in the collecting ducts?

Sodium

What triggers the production of ADH?

Dehydration or blood pressure changes

What is the collecting area shared by?

Nephrons

What goes into the collecting duct is reliant on what?

Hormones

What is osmoregulation?

Osmoregulation is the process that ensures the blood plasma volume and components remain constant - homeostasis.

What does osmoregulation control?

Osmoregulation controls the loss of water and sodium (NaCl).

What does dehydration lead to in terms of blood pressure?

Dehydration leads to decreased blood pressure.

What receptors are involved in detecting increased osmotic pressure?

Osmoreceptors, which are found in the hypothalamus, detect increased osmotic pressure.

What happens when an animal is dehydrated?

When an animal is dehydrated, baroreceptors send messages to the kidneys to respond.

What is the fail-safe mechanism when an animal is dehydrated?

The fail-safe mechanism is decreased blood pressure, which results in less water in the blood.

What does the RAAS system control?

Blood pressure

What is the end goal of the RAAS system?

Increasing blood pressure

What does renin do?

It splits angiotensinogen into angiotensin I.

What is angiotensinogen converted to?

Angiotensin I

How is angiotensin I converted to angiotensin II?

By angiotensin converting enzyme (ACE) produced by the lungs.

What is the effect of angiotensin II?

Causes vasoconstriction of afferent and efferent arterioles.

What does angiotensin II stimulate the release of?

Aldosterone from the adrenal glands.

What is the function of aldosterone?

Increases Na+ reabsorption in the distal convoluted tubule and collecting tubules.

What is antidiuretic hormone (ADH)?

A hormone secreted by the posterior pituitary gland that increases water permeability in collecting ducts.

Where are baroreceptors located?

In the walls of blood vessels.

What do baroreceptors monitor?

Arterial blood pressure.

Where are osmoreceptors found?

In the hypothalamus.

What do osmoreceptors monitor?

The osmotic pressure of the plasma.

How do osmoreceptors affect the body?

They influence the thirst center of the brain and the secretion of ADH.

Renin

An enzyme produced by the kidneys in response to low blood pressure within the arteries

Angiotensinogen

Produced by the liver, converted into angiotensin 1 when it meets renin, only active when needed

What happens to blood pressure when blood is concentrated?

Low blood pressure

What happens to osmotic pressure when blood is concentrated?

Increased osmotic pressure

Which gland secretes increased ADH?

Posterior pituitary gland

What is the effect of ADH on the permeability of collecting ducts?

Increased permeability

What is the result of increased reabsorption of water from the collecting ducts?

Increased volume of extracellular fluid including blood plasma

What is the effect of increased extracellular fluid volume on blood pressure?

Rise in blood pressure

What does ADH stand for?

Antidiuretic Hormone

Where is ADH produced?

Posterior pituitary gland

What effect does alcohol have on ADH?

Inhibits its release, increasing thirst and causing dehydration

What happens to water in the collecting duct when ADH is present?

Water can be reabsorbed and placed back into the bloodstream

What is the role of ADH in blood pressure regulation?

It helps maintain the correct water components of blood for proper pressure