Kidney Function and Hormonal Regulation Quiz

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Questions and Answers

What effect does aldosterone have on urine volume?

Causes urine to become more concentrated

Increases urine volume

Reduces urine volume (correct)

Has no effect on urine volume

How does the medullary portion of the collecting duct participate in water conservation?

It allows more water to leave, concentrating urine (correct)

It is impermeable to water

It increases urine volume

It decreases permeability to water

What occurs in the absence of ADH?

Aquaporins are inserted into the DCT membrane

Aquaporins are taken back into vesicles, leading to dilute urine (correct)

Water is reabsorbed in the collecting duct

Urine becomes more concentrated

Which hormone primarily promotes sodium secretion, resulting in increased water excretion?

ANP Signup and view all the answers

What is the primary role of parathyroid hormone in the kidneys?

Promote calcium reabsorption Signup and view all the answers

What is one of the primary functions of the kidneys?

Filtering blood and excreting toxic metabolic wastes Signup and view all the answers

Which nitrogenous waste is primarily formed from the catabolism of proteins?

Urea Signup and view all the answers

How do the kidneys contribute to the regulation of blood pressure?

By regulating blood volume Signup and view all the answers

What is the primary site of water reabsorption in the nephron?

Descending thin limb of the nephron loop Signup and view all the answers

What is a consequence of prolonged starvation in relation to kidney function?

Synthesis of glucose from amino acids Signup and view all the answers

Which of the following correctly describes the anatomy of the kidneys?

Retroperitoneal and covered by connective tissue layers Signup and view all the answers

Which pressure contributes to the high glomerular filtration rate (GFR)?

Blood hydrostatic pressure (BHP) Signup and view all the answers

How much of the filtered blood is reabsorbed by the nephron?

99% Signup and view all the answers

What primarily influences the filtration pressure across the filtration membrane?

Net hydrostatic and osmotic pressures Signup and view all the answers

What is the glomerular filtration rate (GFR) in mL/min?

125 mL/min Signup and view all the answers

What is the primary function of the urinary bladder?

Temporary storage of urine Signup and view all the answers

Which layer of the bladder wall is made up of transitional epithelium?

Mucosa Signup and view all the answers

What triggers the urine storage reflex in the bladder?

Stretch receptors in the bladder wall Signup and view all the answers

What type of muscle is the detrusor muscle in the bladder composed of?

Smooth muscle Signup and view all the answers

Which structure is responsible for involuntary control of urine flow?

Internal urethral sphincter Signup and view all the answers

How does the female urethra differ from the male urethra?

Angled forward and shorter Signup and view all the answers

What region tends to have persistent infections in the bladder?

Trigone Signup and view all the answers

What happens during the urine voiding reflex?

Parasympathetic neurons stimulate bladder contraction Signup and view all the answers

Which structure is part of the external urethral sphincter?

Skeletal muscle Signup and view all the answers

What is the primary function of the rugae in the bladder?

Allows for expansion of the bladder Signup and view all the answers

What is the normal daily urine output for an average adult?

1-2 L Signup and view all the answers

Which condition is indicated by urine output of less than 500 mL per day?

Oliguria Signup and view all the answers

What is the primary composition of normal urine?

95% water, 5% solutes Signup and view all the answers

Which of the following indicates a concentrated urine sample?

Dark yellow color Signup and view all the answers

What is a possible cause of hematuria, the presence of high levels of red blood cells in urine?

All of the above Signup and view all the answers

Which hormone's absence can lead to polyuria, resulting in urine output exceeding 2 L/day?

ADH Signup and view all the answers

What is the normal pH range for urine, considering a typical diet?

4.5-8.0 Signup and view all the answers

Which of the following substances would be considered abnormal in urine?

Albumin Signup and view all the answers

Which structure in the nephron is primarily responsible for filtering blood plasma?

Glomerulus Signup and view all the answers

What is the primary function of the proximal convoluted tubule (PCT)?

Reabsorption of glucose and amino acids Signup and view all the answers

Which layer of the glomerular capsule consists of simple squamous epithelium?

Parietal layer Signup and view all the answers

What characterizes the descending limb of the nephron loop?

Permeable to water Signup and view all the answers

Which of the following statements about juxtamedullary nephrons is true?

They connect to the vasa recta. Signup and view all the answers

Which segment of the renal tubule is primarily involved in the secretion of undesirable wastes?

Distal convoluted tubule Signup and view all the answers

What function does the filtration membrane serve?

Enables filtration of blood plasma while restricting larger anions Signup and view all the answers

What type of epithelium is found in the collecting duct?

Simple cuboidal epithelium Signup and view all the answers

Which region of the nephron is primarily responsible for the reabsorption of water?

Collecting duct Signup and view all the answers

Which structure acts as the entry point for glomerular filtrate into the renal tubule?

Proximal convoluted tubule Signup and view all the answers

What is the flow pathway of urine from the renal tubule to the outside of the body?

Minor calyx → major calyx → renal pelvis → ureter → urinary bladder → urethra Signup and view all the answers

What characteristic distinguishes cortical nephrons from juxtamedullary nephrons?

Length of loops of Henle Signup and view all the answers

Why is the basement membrane of the glomerulus important?

It repels large anions and plasma proteins. Signup and view all the answers

What type of nephron comprises about 85% of all nephrons and is located primarily in the cortex?

Cortical nephrons Signup and view all the answers

Study Notes

Kidney Functions

Kidneys filter blood and excrete toxic metabolic wastes.
They regulate blood volume, pressure, and osmolarity.
Kidneys regulate electrolytes and acid-base balance.
They secrete erythropoietin, stimulating red blood cell production.
Kidneys help regulate calcium levels through calcitriol synthesis.
They clear hormones and drugs from the blood.
Kidneys detoxify free radicals.
In starvation, they synthesize glucose from amino acids.

Nitrogenous Wastes

Waste is any substance useless to the body or present in excess.
Metabolic waste is a substance produced by the body.
Proteins and nucleic acids contain nitrogen.
When broken down, they are mostly stored as carbohydrates and fats, but some nitrogen remains.
Urea is formed from ammonia, a toxic byproduct of protein catabolism.
Liver converts ammonia to urea.
Uric acid is formed from the metabolism of alcohol and certain foods like seafood.
Creatinine is a byproduct of normal muscle wear and tear.

Excretion

Excretion separates wastes from body fluids and eliminates them.
Four body systems carry out excretion:
- Respiratory system (CO2, water, other gases)
- Integumentary system (sweat, water, inorganic salts, lactic acid, urea)
- Digestive system (water, salts, CO2, lipids, bile pigments, cholesterol)
- Urinary system (metabolic wastes, toxins, drugs, hormones, salts, H+, water)

Kidney Anatomy

Kidneys are retroperitoneal, located behind the peritoneum with ureters, bladder, and adrenal glands.
Right kidney is lower than left due to the liver.
They are covered by three layers of connective tissue: fibrous capsule (protection), perirenal fat (cushions and holds in place), and renal fascia (binds to abdominal wall).

Kidney Gross Anatomy

Outer Renal cortex: outer layer.
Inner Renal medulla: inner layer, with medullary pyramids separated by renal columns.
Renal papilla: pyramids projecting into the renal sinus.
Renal columns: separate pyramids.
Renal sinus: internal cavity containing vessels, nerves, and urine collecting structures.
Lobe of kidney: One renal pyramid, surrounding cortex, and adjacent columns.
Minor calyx: collects urine from the papilla of each pyramid.
Major calyx: convergence of two or three minor calyces.
Renal pelvis: formed by the convergence of two or three major calyces.

Kidney Blood and Nerve Supply

Renal arteries deliver approximately one-quarter (1200 ml) of cardiac output to each kidney per minute.
Arterial and venous flow follow similar paths.
Nerve supply via sympathetic fibers from the renal plexus.

Ureters

Convey urine from kidneys to bladder via peristalsis.
Retroperitoneal.
Enter the base of the bladder through the posterior wall.
No sphincters; pressure increases from distal ends to prevent backflow.
Three layers: mucosa (transitional epithelium and lamina propria), muscularis externa (longitudinal and circular smooth muscle layers), and adventitia (connective tissue).

Urinary Bladder

Muscular sac for temporary urine storage (up to 1 liter).
Retroperitoneal.
Three layers: mucosa (transitional epithelium and lamina propria), muscularis externa (thick detrusor muscle - 3 layers of smooth muscle), and adventitia.
Sphincters: internal (smooth) and external (skeletal).
Rugae: folds in the bladder's wall that allow for expansion.
Trigone: smooth triangular area outlined by the openings of the ureters and urethra. Infections tend to persist in this region.

Urinary Bladder Reflexes

Urine storage reflex: stretch receptors in bladder wall send sensory impulses to the sacral spinal cord when the bladder contains ~200 mL.
Urine voiding reflex: parasympathetic motor neurons stimulate the bladder muscle (detrusor muscle) to contract, and the internal urethral sphincter relaxes.

Bladder Histology

The bladder has a specific epithelium and submucosa.

Urethra

Muscular tube with epithelium varying from pseudostratified columnar to stratified squamous.
Female urethra is short and angled forward (continence supported).
It becomes more vertical in older women (incontinence risk).
Male urethra is longer, and it has three portions: prostatic, membranous, and spongy. Prostatic hypertrophy can lead to retention.

Nephron

Structural and functional units of the kidney (~1.2 million per kidney).
Three functions: filtration, reabsorption, secretion.
Two main parts: renal corpuscle and renal tubule.
Renal corpuscle: filters blood plasma (glomerulus and glomerular capsule).
Renal tubule: converts filtrate into urine.

Filtration Membrane

Glomerular capsule has two layers: parietal (outer) and visceral (inner).
Visceral layer's cells (podocytes) have filtration slits to control the filtrate.
Negatively charged basement membrane repels large anions like plasma proteins.

Renal Tubule

Duct leading from the glomerular capsule to the medullary pyramid tip.
Four regions: proximal convoluted tubule (PCT), nephron loop (U-shaped), distal convoluted tubule (DCT), and collecting duct.

Proximal Convoluted Tubule (PCT)

Longest and coiled region with simple cuboidal epithelium and microvilli for absorption.

Nephron Loop (U-shaped Portion)

Descending and ascending limbs.
Thick segments have simple cuboidal epithelium.
Descending limb is permeable to water; ascending limb is permeable to electrolytes.

Distal Convoluted Tubule (DCT)

Shorter than PCT, w/cuboidal epithelium, often without microvilli.
Reabsorption of water, ions, and secretion of wastes.

Collecting Duct

Receives fluid from several DCTs.
Passes back into the medulla.
Papillary duct: formed from several collecting ducts.

Types of Nephrons

Cortical nephrons: comprise 85% of nephrons; short tubules located in the cortex, delivers to peritubular capillaries (surround entire loop).
Juxtamedullary nephrons: long loops of Henle that deeply invade the medulla, connect to the vasa recta, important in the production of concentrated urine.

Urine Formation: Glomerular Filtration

Kidneys convert blood plasma to urine in four stages: glomerular filtration, tubular reabsorption, tubular secretion, and water conservation.
Glomerular filtrate is similar to blood plasma but without protein.
Urine is fluid that enters the collecting duct.

Forces Involved in Glomerular Filtration

Filtration pressure depends on hydrostatic and osmotic pressures.
BHP (blood): high in glomerular capillaries (60 mm Hg).
Hydrostatic pressure in capsular space (CP): 18 mm Hg due to continual fluid accumulation.
COP (colloid): approximately 32 mmHg.
Net filtration pressure: BHP – CP – COP = 10 mm Hg.

Filtration

Large amounts of blood filtered daily (50-60 times the blood volume in the body).
Glomerular filtration rate (GFR): 125 mL/minute or 45 gallons/day.
Normal filtration depends on good blood flow and normal filtration pressures.

Glomerular Filtration Regulation

3 mechanisms:
- Renal autoregulation (local): nephrons adjust their own blood flow (smooth muscle contracts when stretched).
- Sympathetic control: sympathetic nervous system (vasoconstriction) and constrict afferent arterioles, decrease urine output.
- Hormonal control: Renin (RAAS), water and salt reabsorption.

Hormonal Regulation (Renin)

Renin is secreted when blood flow to the nephron is reduced.
This increases blood pressure and urine production.
Secreted by the Juxtaglomerular Apparatus (JGA) when afferent arteriole BP is low and blood sodium levels are low.

Renin-Angiotensin-Aldosterone System (RAAS)

Stimulated by renin.
Renin converts angiotensinogen (liver) to angiotensin I.
Angiotensin I travels to the lung and is converted to angiotensin II by ACE (angiotensin converting enzyme).
Angiotensin II causes four responses that regulate the body’s fluid balance.

Countercurrent Multiplier

Urine concentration in nephron loop (U shaped).
Descending loop (thin segment) is highly permeable to water.
Ascending limb is permeable to NaCl.
Multiplier = multiplies osmolarity (saltiness) in the medulla.
Countercurrent flow allows collecting duct to concentrate urine and conserve water.

Concentrated Urine

Interstitial fluid near renal papillae is very salty (4X of blood).
Juxtamedullary nephrons aid in creating and maintaining this.
Vasa recta (blood vessels) and urine filtrate flow in opposite directions (important) to regulate concentration and water reabsorption.
Water is reabsorbed and urine becomes highly concentrated.

Tubular Reabsorption

Returns nutrients to blood.
Glucose, amino acids, water, and sodium are reabsorbed to 100%.
Reabsorption happens in:
- Proximal convoluted tubule (PCT) = 65% of filtrate.
- Nephron loop (nephron loop) = 25% of filtrate salts and K+.
- Distal convoluted tubule (DCT) = 7% of initial filtrate.

Transport Maximum

100% of glucose and amino acids are reabsorbed due to facilitated diffusion.
Limited number of carriers, saturation in those carriers can result in blood glucose being detected in the urine (diabetes).

Tubular Reabsorption of Na+

Sodium reabsorption and water follow its path.
Key transport system: symporters and antiporters.
Water follows sodium.
Some substances (amino acids lactate) reabsorbed via symporters with or co-transported with sodium.
Other substances move via antiporters against their concentration gradient.

Tubular Reabsorption and Nitrogenous Wastes

Urea: nephron reabsorbs about half. Concentration remaining in blood is safe.
Uric Acid: PCT reabsorbs but later portions of the nephron secrete.
Creatinine: not reabsorbed because its metabolism is not involved in energy demands, so it is passed in urine.

Tubular Secretion

Occurs primarily in the DCT.
Secretion of potassium, hydrogen, and other ions, compounds, and drugs.

Water Conservation

Collecting duct conserves water and concentrates urine by varying its permeability across the medulla.
Collecting duct is permeable to water.

Basic Stages of Urine Formation

3 stages: glomerular filtration, tubular reabsorption&secretion, water conservation.

Hormones affecting Reabsorption & Secretion

Aldosterone (adrenal cortex): influences sodium and potassium regulation.
Parathyroid hormone (parathyroid gland): regulates calcium reabsorption.
ANP (atrial natriuretic peptide): decreases blood volume and pressure.
Antidiuretic hormone (ADH; hypothalamus): influences water reabsorption in collecting ducts.

Urine Flow

Urine is fine-tuned in the DCT and collecting duct.
Urine flow: minor calyx→major calyx→renal pelvis→ureter (peristalsis)→bladder (“functional valve” that prohibits reflux)→internal urethral sphincter→ urethra.

Urine Characteristics

Urinalysis examines physical and chemical properties.
Color: normally pale yellow (depends on concentration or dyes).
pH: 4.5-8.0 (usually 6.0), varies with diet.
Specific gravity: measure of solutes (density related to water density).
Osmolarity of urine: diluted or concentrated; may correlate with hydration status.
Chemical composition: 95% water; normal solutes (urea, uric acid, creatinine, NaCl, K, Ca, Mg, phosphates, urochrome, bilirubin).
Abnormal solutes include glucose, albumin, ketones (in diabetics = metabolic acidosis). Bile pigments are found in abnormalities.
Urine volume: normal 1-2L/day. Polyuria ( > 2L), oliguria (< 500 mL), and anuria (< 100 mL).

Renal Function Tests

Diagnosing kidney disease; severity assessment & progress monitoring.
Renal clearance tests determine the volume of blood plasma that eliminates particular waste.
Glomerular filtration rate (GFR) assesses kidney disease.
Tests assess substances not secreted or absorbed.

Check Points

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Description

Test your knowledge on kidney functions and the role of hormones in this comprehensive quiz. Explore topics such as aldosterone's effect on urine volume, the medullary portion of the collecting duct, and the influence of ADH on water conservation. Understand how these elements contribute to overall kidney health and efficiency.