urinary system

Urinary system functions

Cleansing blood, pH regulation, blood pressure regulation, solute concentration regulation, red blood cell regulation, vitamin D synthesis.

Kidney failure can result in-

Weakness, lethargy, shortness of breath, anemia, edema, metabolic acidosis, heart arrhythmias

Physical characteristics of urine is affected by

water, nutrient intake, exercise, and environmental temperature

Urinalysis

Helps diagnose kidney diseases

-excessive proteins indicate damage

-excessive quantity can indicate diabetes

Urochrome

Heme-deprived pigment that imparts the typical yellow color of urine

Color of urine can change due to

Dehydration, liver diseases, or obstructions

Polyuria

Excessive urine

>2.5 L/ day

Caused by diabetes, excessive caffeine or alcohol, kidney disease, diuretics, sickle cell anemia, excessive water intake

Oliguria

Below normal urine production

300-500 mL / day

Causes are dehydration, blood loss, diarrhea, cardiogenic shock, kidney disease

Normal production of urine

1-2 L / day

Anuria

Absence of urine produced

50 mL or less a day

Caused by kidney failure or obstruction

Urethra

Transports urine from the bladder to the outside environment, protects surrounding tissue, only urologic organ differing between males and females.

Short in females

Trigone

Base of bladder where ureters originate

Found in the bladder

Bladder

Located retroperitoneal

Highly distensible

Detrusor muscle, transitional epithelium

Micturition

Micturition

Process in which urine empties the bladder

Also called urination or voiding

Detrusor muscle

Smooth muscle in the bladder wall, fibers run in all directions to reduce the size of the organ when emptying it of urine

Sphincter’s

Internal and external urethral sphincters

Can become Incontinent

-control the flow of urine from the urinary bladder

Incontinence

Loss of ability to control Micturition

Ureters

the ureters function via peristalsis, not passive draining

Physiological sphincter at bladder- one way, no reflex

Transitional epithelium with goblet cells

Longitudinal and circular muscles

Kidney

External- contains fibrous capsule outer layer, renal fat pad, adrenal glands on superior aspect

Internal- renal cortex, renal columns, renal medulla, pyramids, papilla, calyces

Renal fat pad

Adipose tissue between the renal fascia and the renal capsule that provides protective cushioning to the kidneys

Calyces

Cup-like structures receiving urine from the collecting ducts where it passes onto the renal pelvis and ureter

Renal hilum

Entry and exit site for renal nerve, vein, and artery

Nephrons

Functional units of the kidney that carry out all filtration and modification to produce urine. Consists of renal corpuscles, proximal and distal convoluted tubules, and descending and ascending loops of henle. Drain into collecting ducts

What does a nephron consist of?

composed of a renal corpuscle (which filters blood) and a renal tubule (which processes filtrate). The specific components include the glomerulus, Bowman’s capsule, proximal convoluted tubule, loop of Henle, and distal convoluted tubule, ultimately draining into a collecting duct. 

What does a renal corpuscle consist of

renal corpuscle includes the glomerulus (a tuft of capillaries) and the surrounding Bowman's capsule. Located in the renal cortex of the kidney, this structure is the initial filtration unit of the nephron, responsible for filtering blood and forming urine. 

Glomerulus

Tuft of capillaries surrounded by bowman’s capsule. Filters the blood based on size

Bowman’s capsule

Cup-shaped sack lined by a simple squamous epithelium (parietal surface) and specialized cells called podocytes (visceral surface) that participate in the filtration process. receives the filtrate, which then passes onto the proximal convoluted tubules

Extension of tubular network covering the glomerulus

Afferent arteriole

tiny blood vessels that carry oxygenated blood to the kidney's glomerulus, which filters blood

Efferent arteriole

Arteriole carrying blood from the glomerulus to the capillary beds around the convoluted tubules and loop of henle. Portion of the portal system.

Loop of henle

Descending and ascending portions between the proximal and distal convoluted tubules. Those of cortical nephrons do not extend into the medulla, whereas those of juxtamedullary nephrons do extended into the medulla

Peritubular capillaries

Second capillary bed of the Renal portal system, surround proximal and distal convoluted tubules, associated with the vasa recta

Vasa recta

Branches of the efferent arterioles that parallel the course of the loops of henle and are continuous with the peritubular capillaries, with the glomerulus, form a portal system

pathway of blood through kidney

Renal artery→ segmental artery→ interlobar artery→ arcuate artery→ interlobular artery→ afferent arteriole→ glomerulus→ efferent arteriole→ peritubular capillaries→ renal vein

Renal cortex

Outer layer, lighter in color than the rest of the organ.

Contains- proximal convoluted tubules, distal convoluted tubules

-cortical nephrons(in cortex, most abundant, short loop of henle)

-Juxtamedullary nephrons (in medulla, long loop of henle)

what are the functional units of a nephron

•form urine from blood filtrate and balance plasma osmolarity while excreting toxins.

3 processes:

1:filtration-takes place in glomerulus.

2:Reabsorption-takes place in peritubular capillaries.

3: secretion

3 secondary process/regulatory functions: 1-blood pressure (via renin). 2- RBC production (via EPO). 3- calcium absorption

Juxtaglomerular apparatus

Located at the juncture of the distal convoluted tubule and the afferent and efferent arterioles of the glomerulus. Plays a role in the regulation of renal blood flow and glomerular filtration rate

Consist of juxtaglomerular cells and macula cells

Juxtaglomerular cells (granular cells)

Modified smooth muscle cells of the afferent arteriole. Secretes renin in response to a drop in blood pressure.

Blood pressure sensors

Macula densa

Cells found in the part of the distal convoluted tubule forming the juxtaglomerular apparatus. Sense sodium concentration in the forming urine

Monitor sodium concentrations and release signals to regulate blood flow

Podocytes

Cells forming finger like processes, form the visceral layer of Bowman’s capsule, pedicels of the podocytes interdigitate to form a filtration membrane

renin

enzyme produced by juxtaglomerular cells in response to decreased blood pressure or sympathetic nervous activity. Catalyzes the conversion of angiotensinogen into angiotensin l.

Regulation of renin release

Macula densa cells also regulate renin release from the JGA.

Renin produces angiotensin l, which gets converted into angiotensin ll in the lungs.

Angiotensin ll is a vasoconstrictor that also prompts the release of aldosterone from the adrenal cortex.

Endocrine regulation - renin

Produced by granular cells of efferent arteriole at the JGA. Converts angiotensin into angiotensin l. Released due to the NO from the JGA and decreased fluid volume.

Endocrine regulation- angiotensin converting enzyme (ACE)

Produced in lungs, binds to afferent arterioles and glomerulus. Converts angiotensin l to angiotensin ll.

Endocrine regulation-Angiotensin ll

Fast acting vasoconstrictor, reduces GFR and renal blood flow, stimulated by decreased blood pressure, prompts release of aldosterone

3 major renal processes

1.glomerular filtration: water and solutes smaller than proteins are forced through the capillary walls and pores of the glomerular capsule into the renal tubule.

2.tubular reabsorption: water, glucose, amino acids, and needed ions are transported out of the filtrate into the tubular cells and then enter the capillary blood.

3.tubular secretion: H, K, creatinine, and drugs are removed from the peritubular blood and secreted by the tubule cells into the filtrate .

Creatinine

A breakdown product of creatine phosphate from muscle and protein metabolism

Proximal convoluted tubule

Microvilli increases surface area for absorption and secretion of solutes

Tortuous tubules receiving filtrate from bowman’s capsule. Most active part of the nephron in reabsorption and secretion

Distal convoluted tubule

Less microvilli and less activity than in the PCT.

Portions of the nephron distal to the loop of henle that receive hyposmotic filtrate from the loop of henle and empty and into collecting ducts

Filtration

Blood filters across glomerular capillaries

Glomerular filtration rate

Volume of filtrate formed by both kidneys per minute.

Influenced by competing pressures

RBCs, WBCs, and large proteins cannot leave the capillaries.

The nephron specializes in 3 processes:

Filtration, reabsorption, and secretion

Net filtration pressure

Sum of all pressures

Pressure of fluid across the glomerulus. Calculated by taking the hydrostatic pressure of the capillary and subtracting the colloid osmotic pressure of the blood and the hydrostatic pressure of bowman’s capsule.