Urinary System and Kidney Structure

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Questions and Answers

What is the primary function of the urinary system related to waste?

Production of red blood cells

Excretion of waste products of metabolism (correct)

Promotion of nutrient absorption (correct)

Regulation of blood sugar levels

Which structure in the kidney is responsible for filtering blood to form urine?

Ureter

Cortex

Nephron (correct)

Renal pelvis

How many major calyces are typically found in one kidney?

Six to seven

Eight to nine

Two to three

Four to five (correct)

What separates the medulla from the cortex in the kidney?

Renal columns Signup and view all the answers

What is the role of erythropoietin in the body?

Stimulation of red blood cell production Signup and view all the answers

What is a characteristic of the renal medulla?

Darker striped appearance due to tubules Signup and view all the answers

What structure does urine pass through after it is collected from the renal pyramids?

Minor calyx Signup and view all the answers

What is the function of the Proximal Convoluted Tubule (PCT) in the nephron?

Reabsorption of substances Signup and view all the answers

What is the primary role of ADH in the kidneys?

Regulates the number of aquaporins and water reabsorption Signup and view all the answers

What percentage of nephrons are cortical nephrons?

85% Signup and view all the answers

Which component of the juxtaglomerular apparatus is involved in regulating blood pressure?

Macula densa Signup and view all the answers

What is the primary function of phagocytosis in the glomerulus?

Remove trapped residues and aggregated proteins from the GBM Signup and view all the answers

Where is erythropoietin synthesized in the kidney?

Endothelial cells of peritubular capillaries Signup and view all the answers

What is a significant characteristic of juxtamedullary nephrons compared to cortical nephrons?

They produce concentrated urine due to longer loops of Henle Signup and view all the answers

Which of the following percentages indicates the reabsorption of glucose in the proximal convoluted tubule?

100% Signup and view all the answers

What distinguishes the descending and ascending parts of the Loop of Henle?

Descending is impermeable to water while ascending is permeable to Na+ Signup and view all the answers

What substances are primarily secreted in the proximal convoluted tubule?

Urea and creatinine Signup and view all the answers

Which segment of the nephron is responsible for the majority of water reabsorption through aquaporins?

Collecting ducts Signup and view all the answers

What is the primary function of the distal convoluted tubule (DCT)?

Reabsorption of electrolytes and secretion Signup and view all the answers

Which layer of Bowman's capsule directly surrounds the glomerulus?

Visceral layer Signup and view all the answers

What feature of endothelial cells in the glomerulus prevents blood cells from passing through?

Fenestrations Signup and view all the answers

Which of the following factors indicates possible damage to the glomerular basement membrane?

Both B and C Signup and view all the answers

What is the role of mesangial cells in the renal corpuscle?

Provide structural support and function in filtration Signup and view all the answers

What is the significance of the filtration barrier in the renal corpuscle?

It selectively allows substances to pass into Bowman's space Signup and view all the answers

How much volume of ultrafiltrate is generally produced per day in the renal corpuscle?

180 L/day Signup and view all the answers

What structural feature do podocytes exhibit to interact with glomerular capillaries?

Interdigitating foot processes Signup and view all the answers

Study Notes

Urinary System

The urinary system consists of the kidneys, ureters, urinary bladder, and urethra.
The urinary system's main functions include excretion of metabolic waste, regulation of blood volume, acid-base balance, electrolyte concentrations, production of renin and erythropoietin, and hydroxylation of vitamin D.

Kidney Structure

The kidney has three layers: cortex, medulla, and renal pelvis.
The cortex is the outer layer, granular in appearance due to the presence of many corpuscles.
The medulla is the inner darker layer, striped in appearance due to the presence of tubules.
The medulla’s structure is subdivided into renal pyramids, which terminate at the papilla. The renal columns are extensions of cortical tissue that separate the pyramids.
The renal pelvis is the expanded upper portion of the ureter.

Renal Lobulations

A renal lobe consists of one medullary pyramid, its surrounding renal column, and overlying cortical tissue.
A renal lobule consists of one central medullary ray and the adjacent cortical labyrinth.

Extrarenal Passageways

Minor calyces are funnel-shaped structures, one for each pyramid, that receive urine from the papilla.
Major calyces are formed by the confluence of minor calyces.
The renal pelvis is formed by the uniting of the major calyces.

Nephron

The nephron is the functional unit of the kidney.
Nephrons are composed of the renal corpuscle, proximal convoluted tubule (PCT), loop of Henle (LOH), and distal convoluted tubule (DCT).

Urine Production

Urine production involves three processes: glomerular filtration, tubular reabsorption, and tubular secretion.

Renal Corpuscle

The renal corpuscle is comprised of the glomerulus and Bowman's capsule.
The glomerulus consists of 10 to 20 capillary loops, supplied by an afferent arteriole and drained by an efferent arteriole.
Glomerular capillaries are lined by fenestrated endothelial cells that allow fluid to pass through, but not blood cells.
The vascular pole is where the afferent arteriole enters and the efferent arteriole exits.
Bowman's capsule is a double-layered epithelial cup that encloses the glomerulus.
The two layers of Bowman's capsule are the parietal and visceral layers.
The parietal layer is composed of simple squamous epithelium and is continuous with the PCT at the urinary pole of the capsule.
The visceral layer consists of podocytes.
Podocytes are modified epithelial cells with primary processes and interdigitating foot processes (pedicles) that interlock and create filtration slits.

Filtration Barrier

The filtration barrier prevents the passage of most blood components into Bowman's space.
The barrier consists of three layers: fenestrated capillary endothelium, the basement membrane, and podocytes.
The glomerular filtration rate (GFR) is approximately 180L/day.
Damage to the filtration barrier can lead to albuminuria (excess protein in the urine) or hematuria (presence of significant amount of blood cells in the urine).

Mesangial Cells

Mesangial cells are located within the renal corpuscle.
Mesangial cells have contractile properties.
Mesangial cells remove debris and aggregated proteins from the filtration barrier, providing structural support, and modulating filtration by contracture.

Tubular Reabsorption

Tubular reabsorption is the process of reabsorbing water, ions, glucose, amino acids, and proteins back into the blood from the tubular lumen.
The PCT is responsible for reabsorbing 65% of Na, Cl, and water, 80% of phosphate and bicarbonate, and 80% of calcium, as well as 100% of glucose and proteins, and 50% of urea.

Tubular Secretion

Tubular Secretion is the process of actively moving substances from the blood into the tubular lumen.
Substances secreted include H, ammonium, creatinine, acetylcholine, dopamine, epinephrine, histamine, fatty acids, and bile acids.

Proximal Convoluted Tubule (PCT)

The PCT is the first segment of the nephron after the renal corpuscle.
It has a cuboidal epithelium with microvilli that greatly increase surface area for reabsorption.
The PCT is responsible for 85% of tubular reabsorption.

Loop of Henle (LOH)

The LOH is a U-shaped structure consisting of a descending limb and an ascending limb.
The descending limb is permeable to water and impermeable to sodium, allowing water to leave the lumen and enter the interstitial space, creating a more concentrated environment.
The ascending limb is impermeable to water and permeable to sodium, allowing sodium to leave the lumen and enter the interstitial space.
The differences in permeability contribute to the concentration of urine.

Distal Convoluted Tubule (DCT)

The DCT is the segment of the nephron after the LOH.
The DCT is responsible for reabsorbing 10% of sodium, chloride, calcium, and bicarbonate.

Collecting Ducts

Collecting ducts are mainly located in the medulla of the kidney.
They reabsorb water (5-25%).
Aquaporins are water channels that facilitate water reabsorption.
Antidiuretic hormone (ADH) regulates the number of aquaporins, controlling water reabsorption.

Blood Supply

The kidneys are highly vascular organs, receiving approximately 25% of the cardiac output.

Nephron Types

Cortical nephrons are the most common type of nephron and are located mostly in the cortex.
Juxtamedullary nephrons have longer loops of Henle that extend deeper into the medulla, allowing excretion of more concentrated urine.

Vasa Recta

The vasa recta is a network of blood vessels that run parallel to the loop of Henle in the medulla.
The vasa recta helps maintain the concentration gradient in the medulla critical for urine concentration.

Endocrine Functions of the Kidney

The kidney has endocrine functions, secreting renin and erythropoietin and activating vitamin D.

Juxtaglomerular Apparatus (JGA)

The JGA is located near the vascular pole of the renal corpuscle.
The JGA plays a key role in regulating blood pressure by activating the renin-angiotensin-aldosterone system (RAAS).
The JGA consists of three major cell types: macula densa, extraglomerular mesangial cells, and juxtaglomerular cells.

Renin-Angiotensin-Aldosterone System (RAAS)

This is a complex hormonal system that regulates blood pressure and fluid balance.
Renin is released from juxtaglomerular cells, which is the first step in the RAAS.
Renin converts angiotensinogen to angiotensin I.
Angiotensin I is converted to angiotensin II by angiotensin-converting enzyme (ACE).
Angiotensin II is a potent vasoconstrictor that stimulates aldosterone release from the adrenal glands.
Aldosterone promotes sodium and water reabsorption in the kidney, leading to increased blood volume and pressure.

Erythropoietin (EPO)

EPO is produced by endothelial cells of peritubular capillaries in the renal cortex.
EPO stimulates red blood cell production in the bone marrow in response to low blood oxygen levels.

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Description

Explore the anatomy and functions of the urinary system, including the kidneys, ureters, and bladder. This quiz covers important topics such as kidney structure, renal lobulations, and the primary functions of the urinary system in maintaining homeostasis.