URINARY SYSTEM CRAM

Glomerulus

High-pressure capillary bed specialized for filtration.

Afferent Arteriole:

large-diameter vessel feeding the glomerulus.

Efferent Arteriole

Smaller-diameter vessel draining the glomerulus (creates back-pressure).

Capsule Parietal Layer:

Simple squamous outer wall of Bowman's capsule

Capsule Visceral Layer

• Inner wall made of podocytes wrapped around the glomerulus.

Pedicels

Foot-like extensions of podocytes.

Slit Pore

Narrow gaps between pedicels that allow filtrate to pass through.

Tubule Epithelium

Mostly simple cuboidal with microvilli (especially in the PCT) for maximum reabsorption.

Juxtaglomerular Apparatus (JGA)

• Definition: Specialized structure where the ascending limb/DCT touches the afferent arteriole. Regulates blood pressure and GFR.

Macula Densa Description

Tall, packed epithelial cells in the DCT wall.

Macula Densa Responds to...

low cl or na + concentrations in filtrate (indicates slow flow).

Macula Densa Effect

Signals JG cells to release renin; vasodilates afferent arteriole.

Juxtaglomerular (JG) Cells Description

Large smooth muscle cells in afferent arteriole wall.

Juxtaglomerular (JG) Cells Responds to...

Drop in blood pressure or Macula Densa signals.

Juxtaglomerular (JG) Cells Effect

Secretes Renin.

Capillary Comparison

• Normal capillaries:

• Low pressure, specialized for exchange of gases/nutrients.

Capillary Comparison

• Glomerular capillaries

High pressure, highly fenestrated (porous), specialized strictly for filtration.

$$\text{Urine=}$$

$$\text{Glomerular Filtration}-\text{Tubular Reabsorption}+\text{Tubular Secretion}$$

Filtration Definition

Passive process where hydrostatic pressure forces water and small solutes out of glomerular blood into Bowman's capsule.

Filtrate Molecules:

Water, glucose, amino acids, urea, uric acid, creatine, and tiny electrolytes (essentially everything in plasma except large proteins and blood cells).

Filtration Pressures

• Favors Filtration:

Glomerular Hydrostac Pressure 55

Oppose Filtration

Capsular Hydrostatic Pressure 15

Glomerular Osmotic Pressure 30

Net Filtration Pressure

GHP - (chp + gop)=10

Significance

• Keeps kidneys filtering wastes continuously to prevent toxic buildup in the blood.

NFP & GFR Relationship:

Direct relationship. If Net Filtration Pressure increases, Glomerular Filtration Rate increases.

Plasma/Filtrate

Glucose, amino acids, and bicarbonate are found in plasma and filtrate,

Tubular Reabsorption Definition

• Moving water and solutes from the renal tubule back into peritubular capillaries.

Where is the majority reabsorbed?

Proximal Convoluted Tubule 65

Tubular Secretion

• Moving substances from the peritubular capillaries into the renal tubule to be excreted in urine.

Substances Secreted:

Hydrogen ions (H+) to regulate pH), Potassium K+, ammonia, drugs (like penicillin), and creatinine.

Autoregulation

Normal resting state where kidneys maintain a constant GFR despite systemic blood pressure changes.

Low BP State

Sympathetic impulses constrict afferent arterioles $\rightarrow$ decreases GFR and decreases urine output (conserves water).

Aging and the Urinary System

• Kidneys shrink (loss of cortical mass).

• Glomerular filtration rate (GFR) drops significantly (often by $50%.

• Renal blood flow decreases as blood vessels lose elasticity.

• Loss of sensitivity to ADH (leads to nocturia/frequent night urination).

• Bladder shrinks and loses muscle tone (leading to incontinence or urinary retention).

Antidiuretic Hormone

Causes the DCT and collecting ducts to reabsorb water (by inserting aquaporins) →increases blood pressure.

Aldosterone

causes na+ reabsorption in the DCT and collecting ducts. Water follows $Na^+$ by osmosis → increases blood volume and increases blood pressure.