ANAPHY - Urinary System

URINARY SYSTEM

Is responsible for removing waste and excess fluids from the body through urine

• urea

• creatinine

• uric acid

Metabolic byproducts our body doesn’t need:

★ pH balance (homeostasis)

Regulates the blood’s pH by (if acidic blood) secreting hydrogen ions (H⁺) → to increase pH of blood

Erythropoietin

promotes RBC production [damage in our kidney = secretion of EPO decreases → decreased EPO = impaired RBC production → leading to anemia]

Activated Vitamin D

Helps the body absorb calcium and phosphate in your gastrointestinal tract (GI tract)

Renin

responsible for the production of aldosterone and angiotensin II (regulates blood volume and blood pressure)

Kidneys

○ One on each side of the spine, just

below the ribcage

(retroperitoneal)

○ Filters blood to remove waste and

excess substances

○ Forms urine

○ Produce hormones

Ureters

○ Muscular tubes that carry urine

from each kidney to the bladder

(connection)

○ Use peristaltic movement to push

urine downward

★ Urinary bladder

○ Stores urine until it's ready to be expelled → contracts urine to Urethra

Urethra

○ Carries urine from the bladder to

the outside of the body during

urination

○ Shorter in females, longer in

males

bean-shaped

Shape of the kidney:

tightly clenched fist (11 cm long, 5 cm wide, 3 cm thick)

Size of kidney:

Renal capsule

(connective tissue) outer layer that protects the kidney → directly attached to a layer of adipose tissue

Renal Hilum

(indentation) entry/exit site for blood vessels, nerves, and the ureter

Renal cortex

Outer region of kidney — where filtration of blood begins

Renal medulla

Inner region that carries filtered fluid toward the renal pelvis (regulation of the concentration of urine)

Renal pyramids

Cone-shaped structures inside the medulla (consists of tubules and ducts → transports and modify fluid into urine)

Minor calyx

Collects urine from a single renal pyramid

Major calyx

Channels urine into the renal pelvis

Renal pelvis

Funnel-shaped cavity that collects urine from the major calyces (connects to the ureter)

Ureter

Tube that carries urine from the

kidney to the bladder

renal artery

Kidney supplies blood through aorta via?

adipose tissues

The yellow layer of tissue surrounding the kidney are what? it serves as a cushion for your kidney

Renal fascia

is a layer of connective tissue that surrounds your adipose tissue and helps anchor your kidney to the abdominal wall

Glomerulus

A ball of capillaries that filters blood

Bowman’s Capsule

Surrounds the glomerulus and collects the filtrate

Proximal Convoluted Tubule (PCT)

(directly connected to renal corpuscle) long segment of renal tubules (located in the cortex) reabsorbs water, ions, glucose, and amino acids back into the blood—secretes toxins and drugs

Loop of Henle

(shaped like a hairpin) this extends into the medulla

Descending limb

reabsorbs water

Ascending limb

reabsorbs salts

Distal Convoluted Tubule (DCT)

Further reabsorption and secretion

Early DCT

Reabsorbs sodium, chloride, and calcium (via PTH), but is impermeable to water

Late DCT

Regulated by aldosterone and ADH, it reabsorbs sodium and water, and helps in acid-base balance

Collecting Duct

○ Collects urine from many nephrons

(many DCT meets in one collecting

duct → this runs through the

medulla) Final water reabsorption

happens here (controlled by ADH)

○ Leads urine toward the renal

papilla → minor calyx → renal

pelvis

Cortical Nephrons

(mostly located in the cortex) shorter than JM nephrons

Juxtamedullary Nephrons

(located near medulla) longer than cortical nephrons

renal corpuscle

is the specialized, spherical structure located in the renal cortex, forming the first part of the nephron and serving as the site of plasma filtration from the blood

Glomerulus

(filters the blood) a tuft of fenestrated capillaries supplied by an aferent arteriole and drained by an eferent arteriole, allowing for high-pressure filtration of blood plasma

Aferent arteriole

(accepts filtrate) The blood vessel that delivers blood to the glomerulus ■ Regulates blood inflow into the glomerular capillaries (a lot of blood comes in)

Eferent arteriole

(exit of filtrate) The blood vessel that drains blood from the glomerulus and carries it to the peritubular capillaries or vasa recta

Bowman’s (glomerular) capsule

a double-walled structure that encloses the glomerulus (all that is needed to be removed from the body goes here)

parietal layer

of simple squamous epithelium forming the outer capsule wall

visceral layer

of specialized cells called podocytes that closely wrap around the glomerular capillaries

glomerular capillaries

are a network of specialized fenestrated (window-like) capillaries located within the glomerulus of the renal corpuscle, and they play a crucial role in the filtration of blood in the kidneys (very porous – has pores)

renal tubules

are a series of microscopic tubes within the nephron that process the filtrate from the glomerulus into urine by performing reabsorption, secretion, and concentration of substances

★ Proximal Convoluted Tubule (PCT)

○ Directly connected to the renal

corpuscle

○ Approximately 14 mm long and

60 micrometer in dm

○ Structure: Highly coiled, lined with

simple cuboidal epithelial cells

rich in microvilli (forming a brush

border) to increase surface area

for reabsorption

★ Loop of Henle (Nephron Loop)

Extends into the medulla

Descending limb

permeable to water, concentrates the filtrate

• is composed

  of simple cuboidal cells and

  becomes simple squamous

  epithelium cells as it thins out

Ascending limb

impermeable to water, actively reabsorbs salts

• starts with squamous epithelium cells and as it thickens, it becomes simple cuboidal cells

★ Distal Convoluted Tubule (DCT)

○ Located in the cortex

○ Composed of simple cuboidal

epithelium (but the cells are

smaller and less microvilli)

★ Collecting Duct

○ Not technically part of a single

nephron but shared by many

○ Receives fluid from multiple DCTs

○ Composed of simple cuboidal

epithelium

○ Larger in diameter than the

tubules

○ Final concentration of urine occurs

here

Filtration

○ Happens in renal corpuscle

○ Blood/Plasma is filtered under

high pressure (glomerulus →

bowman’s capsule)

○ Any substance or solute that

passes through the filtration

membrane (except large molecules

– ex; RBC, albumin)

★ Tubular Reabsorption

Happens mostly in the renal tubules

• Valuable substances like glucose, amino acids, Na⁺, Cl⁻, HCO₃⁻, and water are reabsorbed from the filtrate back into the blood (via peritubular capillaries)

★ Tubular Secretion

○ Happens primarily in the DCT and

collecting duct

○ Waste substances like H⁺, K⁺, NH₄⁺

(ammonium), creatinine, and

certain drugs are actively secreted

from the blood into the tubule

○ Helps in acid-base regulation and

removal of toxins

Glomerular filtration

is the first step in urine formation, where blood plasma is filtered from the glomerular capillaries into Bowman’s capsule in the renal corpuscle (Glomerulus)

Fenestrated endothelium

of the glomerular capillaries (blocks blood cells)

○ Allows free passage of water, ions,

glucose, urea, amino acids, and

small solutes

Basement membrane

– acts as a size and charge barrier (blocks large proteins)

○ Thin layer in between extracellular

matrix (ECM) and capillary

endothelium

○ Can filter blood and plasma based

on their size and charge (charged

selective filter) → size sensitive

Filtration slits

formed by podocytes (from the visceral layer of Bowman’s capsule)

Podocytes

have interdigitating foot processes that form filtration slits

Glomerular Capillary Hydrostatic Pressure (GCHP)

(pressure from aferent arteriole → outward movement, into the glomerular space) The blood pressure within the glomerular capillaries [approximately 50 mmHg] → Promotes filtration

Capsular Hydrostatic Pressure (CHP)

(pushes back the fluid or solutes → inward

movement) The fluid pressure inside

Bowman’s capsule [approximately 10

mmHg] → Opposes filtration

○ ↑Fluid in bowman’s capsule = ↑CHP

= ↓NFP → ↓GFR

Blood Colloid Osmotic Pressure (BCOP)

(pulls water back into the capillaries from

the filtrate) The osmotic pressure created

by (presence of) proteins (mainly

albumin) in the blood within glomerular

capillaries [approximately 30 mmHg] →

Opposes filtration

○ ↑Plasma protein concentration =

↑↓BCOP → ↑↓NFP = ↑↓GFR

Net Filtration Pressure (NFP)

a positive NFP will promote filtration, while a

negative NFP will not provide any

filtration [10 mmHg]

○ NFP = GCHP − (CHP + BCOP)

TUBULAR REABSORPTION & SECRETION

➔ Main site for secretion : DCT ➔ Main site for reabsorption : PCT [65%]

Ultrafiltrate

is the fluid that is filtered from the blood in the glomerulus into the Bowman's capsule during glomerular filtration

★ Active transport

○ Na⁺/K⁺ pump (on basal

membrane):

■ Pumps Na⁺ out of the cell

into interstitial fluid

■ Pumps K⁺ in

■ Uses ATP

■ Creates low Na⁺

concentration inside the

cell, pulling Na⁺ in from the

filtrate → makes

compatible environment for

symport

Symport

○ Na⁺ co-transports other

substances into the cell:

■ Na⁺ + glucose

■ Na⁺ + amino acids

■ Na⁺ + Cl⁻

○ Located on the apical membrane

(facing the tubule lumen)

○ Relies on Na⁺ gradient, not direct

ATP

○ Low intracellular sodium

concentration will drive your

★ Facilitated Difusion

○ Glucose, amino acids, and Cl⁻ exit

the basal membrane into

interstitial fluid → [100% of glucose

and amino acids are reabsorbed]

○ Use carrier proteins (no energy

needed)

○ Moves down concentration

gradient

Osmosis

○ Water follows solutes passively

○ Moves through aquaporin

channels

○ Happens when solute

concentration increases in

interstitial fluid

PROXIMAL CONVOLUTED TUBULE

★ located in the renal cortex and

emerges directly from the Bowman’s

capsule [longest tubule]

★ It's lined with simple cuboidal epithelial

cells that are highly specialized for

absorption

Apical surface

features a brush border made of dense microvilli, vastly increasing surface area for reabsorption [reabsorbs 65% filtrate] → glucose (via SGLT), amino acids, ions, hydrogen ions

★ Thin Descending Limb

○ Epithelium: Simple squamous

○ Permeability: Highly permeable to

water, but impermeable to solutes

(Na⁺, Cl⁻)

○ Function: Water leaves the tubule

by osmosis due to the

hyperosmotic interstitial fluid,

concentrating the tubular fluid.

★ Thin Ascending Limb

○ Epithelium: Simple squamous

(continues from descending limb)

○ Permeability: Impermeable to

water, but permeable to some

solutes (passive Na⁺ and Cl⁻

movement)

○ Function: Solutes (Na⁺, Cl⁻)

passively difuse out of the tubule,

diluting the filtrate

★ Thick Ascending Limb

○ Epithelium: Simple cuboidal with

fewer mitochondria than PCT

○ Transport: Active reabsorption of

Na⁺, K⁺, and Cl⁻ via the Na⁺/K⁺/2Cl⁻

symporter (magnesium and

calcium are also reabsorbed →

dependent on PTH)

○ Impermeable to water → leads to

dilution of the tubular fluid

○ Solute is being reabsorbed → low

concentration (while water is being

retained) → Tonicity of filtrate :

hypotonic (low solute & high

water)

○ Contributes significantly to

medullary hyperosmolarity

★ Left Side – Descending Limb

○ Filtrate flows down the descending

limb of the nephron loop

○ The descending limb is permeable

to water but not to solutes → the

volume of water decreases + retain

solute = water becomes

hypertonic (becomes

concentrated)

○ Water moves out of the tubule by

osmosis into the interstitial fluid

(because it's more concentrated)

○ From there, water enters the

ascending vasa recta, helping to

maintain the medullary

concentration gradient

○ Result: the filtrate becomes more

concentrated as it descends

★ Right Side – Ascending Limb

○ The ascending limb (thin then thick

segments) is impermeable to water

○ However, solutes like Na⁺ and Cl⁻

are reabsorbed into the interstitial

fluid via active and passive

transport

○ Water stays inside the tubule, so

the filtrate becomes more dilute as

it ascends.

○ Solutes that leave the tubule enter

the descending vasa recta,

contributing to the osmotic

gradient in the medulla

Dehydrated

= reabsorption of H2O → tonicity of urine : hypertonic

Hypervolymia

= release H2O → low concentration of ADH → secrete water for excretion

★ Early DCT

○ Adjacent to the loop of henle

(starts in aferent arteriole) →

Located in the renal cortex

○ Impermeable to water →

Hypotonic (further reabsorption of

solutes & water → more solute is

reabsorbed than water)

○ Site for reabsorption of Na⁺ and

Cl⁻ via the Na⁺/Cl⁻ symporter

○ Magnesium and calcium are also

reabsorbed → dependent on PTH

○ Contributes to further dilution of

tubular fluid

★ Late DCT

○ Influenced by hormones

(especially aldosterone and ADH)

○ Contains principal cells and

intercalated cells:

○ Principal cells: involved in Na and

H2O reabsorption and secretion

of K.

Type A

secreting H⁺ (acidotic blood) and reabsorbing HCO₃⁻ (contributes to alkalinity of blood)

Type B

secreting HCO₃⁻ (alkaline blood) and reabsorbing H⁺

Aldosterone

increases Na⁺ reabsorption, K⁺ secretion

ADH (antidiuretic hormone)

increases water permeability

★ Medullary Collecting Duct

○ Final adjustment of urine volume

and osmolality (concentration of

urine)

○ Reabsorption of (same with late

DCT):

■ Water (regulated by ADH)

■ Na⁺ and Cl⁻ (aldosterone)

■ Urea (important for

creating the medullary

osmotic gradient →

hyperosmolarity of

medulla)

○ Secretion of H⁺ and K⁺ as needed

URINE CONCENTRATION

★ Maintain fluid and electrolyte balance and involve complex interactions between nephron segments, hormones, and osmotic gradients in the renal medulla

Countercurrent exchanger (in vasa recta)

○ Water is being secreted while solutes are being reabsorbed → high concentration of filtrate (going down)

Countercurrent multiplier (in loop of Henle)

○ Descending limb: Permeable to

water, not solutes (impermeable to

ion) → water leaves by osmosis

■ Water exits the tubule into

the hyperosmotic medulla,

so the filtrate becomes

more concentrated (up to

1200 mOsm/kg) → some

solutes come in for

concentration

○ Ascending limb: Permeable to

solutes, not water → Na⁺, K⁺, Cl⁻

are reabsorbed

■ Filtrate becomes dilute as it

rises (down to 100

mOsm/kg)

○ It multiplies the osmolarity of the

medulla by pumping solutes out

and keeping water in, establishing

the medullary osmotic gradient

★ Countercurrent exchanger (in vasa recta)

Water is being secreted while

solutes are being reabsorbed →

high concentration of filtrate

(going down)

Future RMT cutie !

○ Water is being reabsorbed while

solutes are being secreted → low

concentration of filtrate (going up)

○ Preserves the osmotic gradient

created by the loop of Henle by

slow blood flow and passive

exchange of solutes and water

○ Descending VR: Water exits into

the medulla, and solutes enter the

blood, increasing osmolarity to

match the medulla

○ Ascending VR: Water re-enters the

blood, solutes exit, and osmolarity

decreases as it returns to the

cortex

★ Nephron Loop: Countercurrent Multiplier

○ Establish osmotic gradient

○ Descending Limb

■ Permeable to water, but not

to solutes

■ Water moves out of the

tubule into the interstitial

fluid via osmosis

■ As water leaves, the filtrate

becomes more

concentrated:

● Osmolarity

increases from 300

→ 600 → 900 →

1200 mOsm/kg

○ Ascending Limb

■ Impermeable to water

■ Actively pumps out Na⁺, K⁺,

and 2Cl⁻ into the interstitial

fluid using a symporter

■ Filtrate becomes less

concentrated as it ascends:

● Osmolarity

decreases from

1200 → 900 → 600

→ 100 mOsm/kg

★ Vasa Recta: Countercurrent Exchanger

○ Maintain osmotic gradient created by countercurrent multiplier

○ Descending VR

■ exits, solutes enter

from the interstitium

■ Blood becomes more

concentrated: 300 → 600

→ 900 → 1200 mOsm/kg

○ Ascending VR

■ Water re-enters, solutes

difuse out (from the

descending limb)

■ Blood is diluted: 1200 →

900 → 600 → 310

mOsm/kg (slightly above

300 to retain some solutes)

★ Renin-Angiotensin-Aldosterone System

plays a key role in regulating the function of the urinary system, regulates blood pressure and blood volume

Renin Secretion

The process begins when the kidneys detect a decrease in blood pressure, low blood volume, or low sodium levels in the distal tubules. In response, juxtaglomerular cells (found in kidney) release renin → will act on angiotensinogen

Angiotensin I Formation

Renin converts a protein produced by the liver called angiotensinogen → angiotensin I. Angiotensin I itself is inactive, but it will soon be converted into a more active form

Angiotensin II Formation

Angiotensin I is converted into angiotensin II by the enzyme ACE (angiotensin-converting enzyme). Angiotensin II is the active hormone that triggers several efects → system will now start working

Aldosterone Release

Angiotensin II stimulates the adrenal glands to release aldosterone (via adrenal cortex), a hormone that acts on the kidneys to increase sodium reabsorption. As sodium is reabsorbed, water follows (due to osmosis), which helps to increase the blood volume and pressure

Vasoconstriction

Angiotensin II causes blood vessels, including those in the kidneys, to constrict, which raises blood pressure by increasing the resistance to blood flow = increase BP

★ Antidiuretic Hormone (ADH) Secretion:

Angiotensin II also stimulates the release of ADH (vasopressin) from the pituitary gland, which acts on the kidneys to promote sodium and water retention, further increasing blood volume and pressure