BIOL204 Anatomy and Physiology Exam 3 - Spring 2025

What are the organs of the urinary system?

kidneys, ureters, urinary bladder, urethra

Kidney

organ that filters the blood to remove metabolic wastes, toxins, and more, producing urine

Ureters

tubes that connect the kidneys to the urinary bladder

Urinary Bladder

organ that stores the urine

Urethra

tube through which urine is expelled from the body

Where are the kidneys located in the body?

against the posterior abdomen wall

The organs of the urinary system are organs of ______

excretion

What are the primary functions of the kidneys?

synthesis of essential substances, filtration of blood, and regulation of water, electrolytes, acids and bases, and blood pressure

What do kidneys synthesize?

erythropoietin, calcitrol, renin

What do kidneys filter out?

urea, creatinine, uric acid, bilirubin, ingested toxins

How do kidneys balance water and electrolytes?

reabsorbing or excreting water as needed

How do kidneys balance acids and bases?

excreting excess carbonic acid or ammonia

Nephron

the structural and functional units of the kidneys

How many nephrons are found in each kidney?

over 1 million

What are the two types of nephrons?

cortical and juxtamedullary

Juxtamedullary Nephrons

reside closer to the medulla with a role in urine concentration

Cortical Nephrons

predominantly located in the outer cortex of the kidney

Juxtamedullary nephrons make up __% of all nephrons

15

Cortical nephrons make up __% of all nephrons

85

Each nephron consists of...

renal corpuscle and renal tubule

Function of the Renal Corpuscle

filters blood plasma

Function of the Renal Tubule

converts filtrate into urine

The Renal Corpuscle consists of...

Bowman's capsule and the glomerulus

Bowman's Capsule

cup-shaped hollow structure that completely surrounds the glomerulus

Glomerulus

a knot of capillaries wrapped by podocytes, where blood enters the nephron

Glomerular Filtration

a process in which water and some solutes in the blood plasma pass from capillaries of the glomerulus into the capsular space of the nephron

What is the first step of glomerular filtration?

blood enters the glomerulus via the afferent arteriole

What is the second step of glomerular filtration?

due to higher pressure in the glomerulus compared to the capsule space, water and small solutes like glucose and waste products are pushed out

What is the third step of glomerular filtration?

filtrate forms and collects in the capsular space around the glomerulus

What is the fourth step of glomerular filtration?

blood exits through the efferent arteriole and the filtrate continues to the renal tubule

Net Filtration Pressure

the total pressure that promotes filtration

Glomerular Hydrostatic Pressure (GHP)

blood pressure in the glomerular capillaries, around 55 mmHg

Glomerular Colloid Osmotic Pressure (GCOP)

pulls water back into glomerular capillaries, around 30 mmHg

Capsular Hydrostatic Pressure (CHP)

pushes back on glomerular membrane, around 15 mmHg

Calculating Net Filtration Pressure

GHP - (GCOP + CHP)

What is the average net filtration pressure?

10 mmHg

Filtration Membrane

interface between the glomerulus and the nephron

What are the three barriers of the filtration membrane?

fenestrated endothelium, basement membrane, and filtration slits

Fenestrated Endothelium of Glomerular Capillaries

very small pores that prevent filtration of blood cells

Basement Membrane of Glomerulus

restricts passage of large plasma proteins, consisting of proteoglycan gel

Filtration Slits between Pedicels

negatively charged, being an obstacle for large anions; prevents the filtration of medium-sized proteins

Podocytes

cells in the Bowman's capsule in the kidneys that wrap around capillaries of the glomerulus

What molecules can pass the filtration membrane?

amino acids, glucose, nitrogenous waste, small ions, water

What molecules canNOT pass the filtration membrane?

blood cells, plasma proteins

Nitrogenous Wastes

urea, uric acid, creatinine, ammonia

Ammonia

toxic byproduct of protein catabolism that is converted to urea in the liver

Urea

byproduct of protein catabolism, about 50% of nitrogenous waste

Uric Acid

byproduct of nucleic acid catabolism

Creatinine

byproduct of creatine breakdown

Glomerular Filtration Rate

the amount of filtrate formed per minute by the two kidneys combined

What is the average GFR for males?

125 mL/min, 180 L/day

What is the average GFR for females?

105 mL/min, 150 L/day

What happens if you have low GFR?

fluid is flowing slowly through the renal tubules, so they may reabsorb waste that should be excreted

What happens if you have high GFR?

fluid is flowing too rapidly through the renal tubules for them to reabsorb water and solutes, leading to dehydration and electrolyte depletion

Intrinsic Controls of Glomerular Filtration

involves local responses initiated and maintained by the kidneys that directly affect GFR despite changes in BP

Extrinsic Controls of Glomerular Filtration

can be either neural or hormonal, operating through the whole system and respond to significant changes in BP, with the purpose of preventing any damage to vital organs

What kind of mean arterial blood pressure would the extrinsic GFR controls respond to?

<80 mmHg

Intrinsic Controls of Glomerular Filtration Examples

myogenic response, tubuloglomerular feedback

Extrinsic Controls of Glomerular Filtration Examples

neural (sympathetic) and hormonal (angiotensin II)

Myogenic Mechanism

when BP rises, the increased pressure against the walls of the afferent arteriole triggers stretch receptors, leading to vasoconstriction, preventing excessive blood flow into the glomerulus; relies on the tendency of smooth muscle to contract when stretched

Tubuloglomerular Feedback

involves the juxtaglomerular apparatus; in response to the threat of urinary salt loss, it triggers vasoconstriction, reducing filtration by producing adenosine through the hydrolysis of nucleotide precursors like ATP

Juxtaglomerular Apparatus

specialized cells next to the glomerulus, including the macula densa, mesangial cells, and granular cells

Macula Densa

part of a tubular area that senses tubule flow, particularly the concentration of NaCl; when GFR increases, leads to a rise in NaCl concentration, & cells secrete ATP

Mesangial Cells

located within the glomerulus and positioned between the capillaries, metabolize ATP into adenosine

Granular Cells

responsible for producing renin; modified smooth muscle cells wrapped around the afferent arteriole. In response to adenosine, they constrict the arteriole

Renin-Angiotensin-Aldosertone System (RAAS)

plays a role in the regulation of blood pressure, involving several steps and components

What is the first step of the RAAS?

a decrease in systemic blood pressure leads to a corresponding decrease in GFR

What is the second step of the RAAS?

juxtaglomerular cells release renin into the bloodstream

What is the third step of the RAAS?

renin converts angiotensinogen into angiotensin-I, which remains inactive

What is the fourth step of the RAAS?

angiotensin-converting enzyme (ACE) converts angiotensin-I into the active form, angiotensin-II

What is the fifth step of the RAAS?

angiotensin-II, now in its active state, functions to restore fluid volume and blood pressure

Angiotensinogen

a plasma protein produced by the liver and converted by renin to angiotensin I

Renin

hormone secreted by the kidney that raises blood pressure

Angiotensin-I

Inactive precursor converted to angiotensin II

Angiotensin-Converting Enzyme

enzyme that converts angiotensin I to angiotensin II

Angiotensin-II

hormone that acts to restore fluid volume and BP

What are some effects of Angiotensin II?

- promotes vasoconstriction of efferent arterioles and systemic blood vessels

- promotes reabsorption of sodium and chloride ions from the proximal tubule

- promotes aldosterone release

- stimulates the thirst center in the hypothalamus

What path does fluid flow in the renal tubule?

proximal convoluted tubule --> Loop of Henle --> distal convoluted tubule --> collecting duct --> papillary duct

Proximal Convoluted Tubule

the first segment of the renal tubule where reabsorption of water, ions, glucose, amino acids, etc. occurs

Distal Convoluted Tubule

follows the Loop of Henle, shorter and more coiled than PCT, where further fine-tuning of electrolyte balance occurs

Loop of Henle

a U-shaped segment that dips into the medulla that plays a crucial role in concentrating urine

Collecting Duct

receives fluid from multiple nephrons, adjusts water reabsorption based on the body's hydration status

Papillary Duct

originate in the renal pyramids of the kidney, responsible for collecting urine from the renal papillae

What path does fluid flow from the papillary duct to the bladder?

papillary duct --> minor calyx --> major calyx --> renal pelvis --> ureter --> bladder

Minor Calyx

a cup in which the papilla of each renal pyramid is nestled, collects urine

Major Calyx

2-3 minor calyces converge

Renal Pelvis

where 2-3 major calyces converse in the sinus

What are the major renal processes in urine production?

tubular reabsorption, glomerular filtration, tubular secretion, water excretion and conservation

Tubular Reabsorption

the process of selectively moving substances from the filtrate back into the blood; anything not reabsorbed becomes urine

Tubular Secretion

the process of selectively moving substances from the blood into the filtrate

The ___ is the most metabolically active site of reabsorption

proximal convoluted tubule

Paracellular Route

substances pass through gaps between the cells

Transcellular Route

substances pass through the cells of the tubules

The ___ route is primarily for small ions and water

paracellular

The ___ route utilizes sodium-potassium pumps

transcellular

Apical Membrane

the surface of the plasma membrane that faces inward to the lumen

Basolateral Membrane

faces the interstitial fluid and is indirectly in contact with the blood

Transport Maximum (Tm)

the maximum rate of reabsorption, which is reached when transport proteins are saturated

Normoglycemia

normal blood sugar levels; normal urine volume, glucose-free

Hyperglycemia

high blood sugar, transport proteins cannot absorb all glucose, increased urine volume