Week 24a: Urinary System

What are the three main functions of the urinary system?

The three main functions of the urinary system are excretion, elimination, and osmoregulation.

What is excretion?

Excretion is the process by which metabolic waste products are removed from body fluids.

What is elimination?

Elimination is the process by which urine is removed from the body.

What is osmoregulation?

Osmoregulation is the process by which the urinary system regulates the water concentration in the blood.

What are the four components of the urinary system?

The four components of the urinary system are the kidneys, the urinary tract, the urinary bladder, and the urethra.

What is the function of the kidneys?

A pair of kidneys - these are highly vascularized and are attached to the aorta and the inferior vena cava. The basic functional unit of the kidneys is the nephron (1million each kidney). These filter metabolic waste from the blood and convert it to urine.

What is the urinary tract?

The urinary tract is made of two ureters that connect the kidneys to the urinary bladder.

What is the urinary bladder?

The urinary bladder is a muscular and elastic organ that temporarily stores urine.

What is the urethra?

The urethra is the part of the urinary system that connects the bladder to the external environment. In men, it also carries sperm.

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What are the four additional homeostatic functions of the urinary system?

The four additional homeostatic functions of the urinary system are regulation of blood volume and pressure, regulation of blood ionic concentration, maintenance of blood pH, and conserving glucose and amino acids.

What is the urinary system's role in regulating blood volume and pressure?

The urinary system regulates blood volume and pressure by altering blood water concentration through the production of urine.

How does the urinary system regulate blood ionic concentration?

The urinary system regulates blood ionic concentration by selectively reabsorbing or secreting ions such as sodium, potassium, and calcium.

How does the urinary system maintain blood pH?

The urinary system maintains blood pH by regulating the excretion of hydrogen ions and bicarbonate ions in the urine.

How does the urinary system conserve glucose and amino acids?

The urinary system conserves glucose and amino acids by selectively reabsorbing them back into the bloodstream during urine formation.

What are the hormones produced by the urinary system and what are their roles?

The urinary system produces erythropoietin, which stimulates the production of red blood cells, and renin, which regulates blood pressure. The kidneys also produce calcitriol, which regulates calcium concentration in the blood.

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Where are the kidneys located in the abdominal cavity?

The kidneys are located in the abdominal cavity between the T12 and L3 vertebrae.

Which kidney sits slightly lower, the left or right?

The right kidney sits slightly lower than the left kidney.

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What is the location of the adrenal glands in relation to the kidneys?

The adrenal glands are located on the superior surface of both kidneys.

What is the anatomical relationship between the kidneys, adrenal glands, body wall, and peritoneal lining?

The kidneys and adrenal glands sit between the body wall and the peritoneal lining, and they are retroperitoneal.

What are the three structures that help maintain the position of the kidneys?

The three structures that help maintain the position of the kidneys are the peritoneum, contact with adjacent organs, and connective tissue (renal fascia).

What can happen if there is damage to the structures that help maintain the position of the kidneys?

Damage to the structures that help maintain the position of the kidneys can cause a condition known as "floating kidney," where the kidneys move out of their normal position.

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What is the color of the kidney?

The kidney is reddish-brown.

What are the average dimensions of a human kidney?

The average human kidney is 10cm long, 5.5cm wide, and 3cm thick.

What is the average weight of a human kidney?

The average human kidney weighs 150g.

How much of the cardiac output does the kidney receive?

The kidney receives 20-25% of all cardiac output.

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What is the renal hilum?

The renal hilum is a recess in the kidney that serves as an entry point for the renal arteries and nerves, and an exit point for the renal veins and ureters.

What is the function of the fibrous capsule in the kidney?

The fibrous capsule provides an anchor to surrounding tissues and also lines the renal sinus, which is a large cavity that contains many other structures.

What structures enter and exit the kidney through the renal hilum?

The renal arteries and nerves enter the kidney, while the renal veins and ureters exit the kidney through the renal hilum.

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What are the two major layers of the kidney and how are they divided?

1. The renal cortex is the outer layer and it makes direct contact with the fibrous capsule. The renal cortex extends as renal columns (of Bertin) into medulla in between pyramids allows the cortex to be better anchored.
2. The renal medulla is the inner layer and it is divided into renal pyramids. Each kidney contains 6 to 18 renal pyramids where the majority of the nephrons are found. The tip of the renal pyramid is called the renal papilla.

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What structures does urine pass through as it travels from the renal pyramids to the renal pelvis?

Urine made in renal pyramids enters minor calyxes, then flows into major calyxes, and ultimately into the renal pelvis.

What is the renal pelvis and what is its function?

The renal pelvis is a funnel-like structure and it forms the upper dilated part of the ureter. When it distends, peristalsis occurs and urine is moved from the kidneys to the urinary bladder.

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What is a kidney lobe?

A kidney lobe is the basic functional unit of the kidney consisting of a single renal pyramid and its surrounding renal cortex.

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What happens to urine produced by nephrons?

Urine produced by nephrons enters a collecting duct in the renal pyramid.

What happens to collecting ducts?

Collecting ducts converge to form the papillary duct.

Where does the papillary duct extend through?

The papillary duct extends through the renal papilla into the minor calyx associated with the kidney lobe.

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What percentage of cardiac output do the kidneys receive?

The kidneys receive 20-25% of all cardiac output.

How much blood do the kidneys filter per minute?

The kidneys filter 1.2L of blood every minute.

Where do the renal arteries branch off from?

The renal arteries branch directly off the abdominal aorta.

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Where do the renal arteries branch from?

The renal arteries branch from the aorta.

What happens after the renal arteries bifurcate?

After the renal arteries bifurcate, they divide further.

Where do the interlobar arteries start and what do they supply?

The interlobar arteries start in the renal sinus and extend into the renal cortex. They supply blood to the arcuate arteries.

What are the arcuate arteries and where are they located?

The arcuate arteries are arteries that hug the boundary of the cortex and medulla.

What do the cortical radiate arteries supply and what do they originate from?

The cortical radiate arteries supply the renal cortex with blood and originate from the arcuate arteries.

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What do the cortical radiate arteries divide further into and what do they supply?

The cortical radiate arteries divide further into afferent arterioles, which supply blood to the nephrons.

How does blood leave the nephron and where does it enter next?

Blood leaves the nephron through the efferent arteriole and enters the peritubular capillary network.

What occurs at the peritubular capillary network?

At the peritubular capillary network, substances are exchanged between the blood and the kidney.

What is the vasa recta and how does it connect to the peritubular capillaries?

The vasa recta is a network of capillaries that runs parallel to the nephron loop and connects to the peritubular capillaries.

What does juxta mean?

Near

What do juxtamedullary nephrons have that penetrate deep into the medulla?

Juxtamedullary nephrons have collecting ducts that penetrate deep into the medulla.

How does the venous system of the kidney compare to the arterial system?

The venous system of the kidney exactly mirrors the arterial system, and blood is taken back to the abdominal vena cava.

What structure converges with the vasa recta and where does it lead to?

The vasa recta converges with the cortical radiate veins and leads back to the renal vein.

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What structure converges with the cortical radiate veins?

The vasa recta converges with the cortical radiate veins.

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What is the basic functional unit of the kidney?

The nephron is the basic functional unit of the kidney.

What are the two substructures that make up each nephron?

Each nephron consists of two substructures

the renal corpuscle, which includes the glomerular (Bowman's) capsule, and the juxtaglomerular complex

the renal tubule which includes the proximal convoluted tubule (PCT), the nephron loop (loop of Henle), and the distal convoluted tubule (DCT).

What is the juxtaglomerular complex?

The juxtaglomerular complex is a structure in the kidney that regulates blood pressure and the filtration rate of the glomerulus.

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What is the renal corpuscle and what happens there?

The renal corpuscle is a substructure of the nephron in the kidney where ultrafiltration occurs. Blood is forced through the glomerulus, a capillary network that forces red blood cells through in single file. Fenestrations in the capillary wall and surrounding epithelium allow passage of water, ions, and nutrients into the capsular space of the Bowman's capsule.

What is the size of each renal corpuscle?

Each renal corpuscle has a 200μm diameter.

How does blood enter and leave the glomerulus?

Blood enters the glomerulus via the afferent arteriole and leaves via the efferent arteriole.

Is ultrafiltration in the renal corpuscle selective or non-selective?

Ultrafiltration in the renal corpuscle is non-selective, meaning useful products such as glucose, amino acids, and fatty acids are lost to the filtrate.

How is reabsorption of lost products from ultrafiltration accomplished?

Reabsorption of lost products from ultrafiltration occurs in the renal tubule.

What is the role of the proximal convoluted tubule (PCT)?

The PCT attaches to the Bowman's capsule and reabsorbs water and ions.

What is the loop of Henle and what are its different roles?

The loop of Henle is a part of the renal tubule that extends deep into the medulla and has two limbs with different roles. The descending limb is permeable to water but not ions, and the ascending limb is permeable to ions but not water.

Where does the distal convoluted tubule (DCT) attach, and what is its role?

The DCT attaches to the collecting system and is responsible for further reabsorption of ions and the secretion of waste products.

Does the composition of tubular fluid remain constant throughout the renal tubule?

No, the composition of tubular fluid changes throughout the renal tubule due to reabsorption and secretion processes.

Is the composition of urine at the renal corpuscle similar to that which enters the renal pelvis?

No, the composition of urine at the renal corpuscle is very different from that which enters the renal pelvis.

What happens during ultrafiltration at the renal corpuscle?

During ultrafiltration at the renal corpuscle, nearly everything is forced out of the blood.

What are the three functions of nephrons?

Nephrons allow reabsorption and alteration of urine composition by fulfilling three functions

1\.Reabsorption of useful nutrients

2\.Reabsorption of 90% of water from filtrate

3\.Secretion of waste products that were not removed by ultrafiltration

What are the three structures that make up the Bowman's capsule?

The three structures that make up the Bowman's capsule are:


1. Parietal layer of simple squamous epithelium that is continuous with...
2. The visceral epithelium made of podocytes which surround the capillaries of the glomerulus. Beneath the visceral layer lie the glomerular capillaries.
3. The gap between the two epithelial layers is the Bowman's/urinary space.

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What is the glomerulus and how does it relate to the Bowman's capsule?

The glomerulus is a capillary network inside the Bowman's capsule that forces blood through in single file. The capillary epithelium is fenestrated and blood enters at high pressure, causing the filtrate in the capsular space to contain lots of solutes and water that must be reabsorbed.

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What is the role of podocytes in the Bowman's capsule?

Podocytes surround the capillary epithelium in the glomerulus and their foot-like processes attach to the basement membrane. They prevent the filtration of red blood cells and plasma proteins by forming a barrier with small gaps between their podocytes. Solutes must fit through capillary pores, basement membrane fibers, and the gaps between podocytes to enter the filtrate in the capsular space.

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What is the PCT and where does it connect to?

The PCT stands for the proximal convoluted tubule and it connects to the capsular space, which is the point at which filtrate enters the renal tubule.