Chapter 26 The Urinary System Flashcards
Functions of the Urinary System
- Excretes waste products
- Regulates composition of blood
- Produces Renin
- Produces Erythropoietin
- Activates Vitamin D
- Gluconeogenesis
Functions of the Urinary System: Excretes waste products
like urea, uric acid, creatinine (nitrogenous wastes, made by our body)
Functions of the Urinary System: Regulates composition of Blood
ions, pH, blood volume (how much water)
Functions of the Urinary System: Produces Renin
(enzyme)
Angiotensinogen— Renin by kidneys—> Angiotensin 1 (inactive)—– ACE made by lungs–> Angiotensin II
- occurs when blood pressure is to low
- Angiotensin II causes vasoconstriction
- ACE= angiotensin converting enzyme
Functions of the Urinary System: Produces erythropoietin
in response to low oxygen levels
-erythropoietin stimulates erythropoiesis to make more RBCs made by the red bone marrow which will carry more oxygen
Functions of the Urinary System: Activates Vitamin D
Skin makes (inactive) Vitamin D—> Liver Vitamin D–> active Vitamin D activated by the Kidneys
Functions of the Urinary System: Gluconeogenesis
conversion of noncarbohydrates (fats) into glucose
What are the organs that perform the functions of the urinary system?
The Kidneys
The other structures of the urinary system that store or carry urine out of the body are?
- ureters
- urinary bladder
- urethra
Anatomy of the Kidney
- Retroperitoneal- located between dorsal body wall and parietal peritoneum
- 3 layers of supportive tissue:
1. Renal Fascia
2. Adipose Capsule
3. Renal Capsule
3 Main Regions of the Kidney
- Renal Cortex
- Renal Medulla
- Renal Pelvis
What are the structural and functional units of the kidneys?
Nephrons
-there are over 1 million nephrons per kidney
Structure of a Nephron
- Renal Corpuscle
2. Renal Tubules
Structure of a Nephron: Renal Corpuscle
- filtration of blood takes place here
- consists of:
a. Glomerulus
b. Bowman’s Capsule
Structure of a Nephron: Renal Tubules
- Filtrate is processed to form urine
- consists of:
a. Proximal Convoluted Tubule (PCT)
b. Loop of Henle
c. Distal Convoluted Tubule (DCT)
2 kinds of Nephrons
- Cortical Nephrons
2. Juxtamedullary Nephrons
2 kinds of Nephrons: Cortical Nephrons
- 85% of all nephrons
- Most of the nephron located in cortex of kidney
- Have short Loops of Henle
2 kinds of Nephrons: Juxtamedullary Nephrons
- 15% of all nephrons
- Most of the nephron located near the border between the cortex and medulla of kidney
- Have long Loops of Henle
Nephrons have 2 Capillary Beds
- Glomerulus- exchanges with Bowman’s capsule (filtration)
2. Peritubular Capillaries- exchange with the renal tubules (reabsorption and secretion)
Nephrons have 2 Capillary Beds: Glomerulus
exchanges with the Bowman’s capsule (filtration)
Nephrons have 2 Capillary Beds: Peritubular Capillaries
exchange with the renal tubules (reabsorption and secretion)
-Vasa Recta are peritubular capillaries that exchange with the long Loops of Henle
Flow of Blood Through the Kidneys
Renal Artery—-arteries—> afferent arterioles—->glomerulus (filtration)—->efferent arterioles—> peritubular capillaries or vasa recta (reabsorption and secretion)—>veins—>renal vein
Flow of Filtrate through the Kidneys
Filtrate forms in Bowman’s Capsule—-> PCT—> descending limb of loop of Henle—> ascending limb of loop of Henle—> DCT—> Collecting Ducts
Filtrate
fluid that enters the Bowman’s capsule and flows through the renal tubules
Urine
fluid leaving the collecting ducts
Kidney Physiology
- Blood flow through kidneys= 1200ml/min
- GFR (rate of filtrate formation)= 120ml/min
- Rate of urine formation= 1.2ml/min
Kidney Physiology: Blood flow through kidneys
1200ml/min
Kidney Physiology: GFR (rate filtrate formation)
120ml/min
Kidney Physiology: Rate of urine formation
1.2ml/min
3 Steps in Urine Formation
- Glomerular Filtration- makes filtrate
- Tubular Reabsorption- substance leave filtrate and enter the blood in peritubular capillaries
- Tubular Secretion- substances leave the blood in peritubular capillaries and enter filtrate
Glomerular Filtration
- passive, nonselective process
- Hydrostatic pressures force fluids across filtration membrane
- Fluids move out of the glomerulus and into the Bowman’s Capsule
The Filtration Membrane is
- Very Thin- 0.1 micrometers
- Very Permeable- consists of:
a. fenestrated capillaries (wall of glomerulus, has pores and clefts, very leaky)
b. Podocytes (inner wall of the Bowman’s capsule, has filtration slits)
c. basal lamina
Glomerular Blood Hydrostatic Pressure (GBHP) is
55mmHg
NFP= HP(glomerulus) - (OP (glomerulus + HP (capsule)) NFP= +, then? NFP= -, then?
If NFP= +, then filtration occurs
if NFP= -, then reabsorption occurs
Regulation of Glomerular Filtration
- Myogenic Mechanism
- Macula Densa Cells- chemoreceptors in ascending limb
- Juxtaglomerular Cells- secrete Renin
What is secreted by Juxtaglomerular cells due to low blood pressure in glomerulus?
Renin
Angiotensinogen–renin–> angiotensin I—ACE–> angiotensin II
Tubular Reabsorption
- 99% of water and many solutes in the filtrate return to the blood
- the chemical composition of the filtrate is adjusted
Tubular Secretion
- substances in the blood in the peritubular capillaries enter the filtrate in the renal tubules and collecting ducts
- helps get rid of waste products
- helps maintain blood pH
What happens in the first and second capillary beds?
1st- filtration
2nd- tubular reabsorption + tubular secretion
Regulation of Glomerular Filtration: Myogenic Mechanism
-smooth muscle cells of afferent arteriole
able to dilate or constrict, automatically adjust diameter to make sure pressures are right
Regulation of Glomerular Filtration: Macula Densa Cells
chemoreceptors of the ascending limb (detect chemical composition of filtrate to adjust pressures going through glomerulus)
-detect chemically adjustment of afferent arterioles
Regulation of Glomerular Filtration: Juxtaglomerular Cells
pressure sensors detect low pressures and will produce Renin (enzyme)
Angiotensinogen—Renin–> Angiotensin I—-> ACE—> angiotensin II
-angiotensin II causes vasoconstriction; increase blood pressure throughout the body and kidneys
Filtrate Contains
- water
- wastes (urea, uric acid, creatinine)
- Ions (Na+, K+, Cl-, Ca+2, Mg+2)
- Nutrients (glucose, amino acids, vitamins, lipids)
Tubular Reabsorption in different parts of the renal tubule
PCT
Long Loops of Henle
DCT + Collecting Ducts
Tubular Reabsorption in different parts of the renal tubule: PCT
most of selective reabsorption occurs here (select what gets back into the blood)
-driven by the active transport of Na+
Tubular Reabsorption in different parts of the renal tubule: Long Loops of Henle
Reabsorption generates osmotic gradients in medulla
Tubular Reabsorption in different parts of the renal tubule: DCT + Collecting Ducts
reabsorption mainly regulated by hormones
PCT Tubular Reabsorption
Mechanism
Na+ Primary active transport (Na+ K+ pump)
Glucose, Secondary Active transport, use
amino acids, specific carriers
vitamins
Water Osmosis by Obligatory water
reabsorption
Some ions Passive, Paracellular
Urea, Uric Acid
Lipids (lipid-soluble Passive, no specific carriers
substances)
Proteins Endocytosis & digested to amino
acids
Creatinine Not Reabsorbed
Long Loops of Henle Tubular Reabsorption
Descending Limb: water reabsorbed to blood (lose water, water comes out)
Ascending Limb: solutes reabsorbed to blood (lose solutes, solutes leave)
Generates osmotic gradients in medulla (300- 1200 mOsmolar) Descending Limb is: -permeable to water -impermeable to solutes Ascending Limb is: -permeable to solutes -impermeable to water
DCT & Collecting Ducts Tubular Reabsorption
Regulated by Hormones
Water Osmosis by facultative water
reabsorption needs ADH
Na+ Active transport of Na+ needs
ALDOSTERONE
Urea Passive, urea leaks out in deep
parts of medulla
Tubular Secretion of Certain drugs, Urea & Uric Acid, H+ or bicarbonate ions, K+ ions
Secretion of: Located: Function:
Certain Drugs PCT Rid body of drugs
(Penicillin)
Urea &
Uric Acid PCT Rid body of waste products
H+ or bicarbonate
ions PCT Regulate blood pH
K+ ions DCT & Collecting ducts Regulates blood K+
Osmolarity
of solute particles per 1 liter of water
- a measure of a solution’s ability to cause osmosis (water movements)
- body fluids are maintained at 300 mOsm
Formation of Dilute Urine
- Stimulus is excess water in the body (low osmolarity <300 mOsm in plasma)
- ADH release is inhibited; collecting ducts are impermeable to water
- No facultative water reabsorption
- Large volume of dilute urine excreted
Diuretic
substances that increase urine output
Formation of Concentrated Urine needs
- Medullary osmotic gradient (300- 1200 mOsm)
- Antidiuretic hormone (ADH) which causes collecting ducts to be permeable to water
Formation of Concentrated Urine
- Stimulus is dehydration (high osmolarity, >300mOsm in plasma)
- ADH is released; collecting ducts permeable to water
- Facultative water reabsorption occurs
- Small volume of concentrated urine excreted
Countercurrent Mechanism
Osmotic gradients in the medulla are mainly due to the countercurrent mechanism
It consists of:
a. Countercurrent Multiplier- Long Loops of Henle which generate the gradient
b. Countercurrent Exchanger- Vasa Recta which maintains the gradient
Countercurrent Mechanism: Countercurrent Multiplier
Long Loops of Henle which generate the gradient
Countercurrent Mechanism: Countercurrent Exchanger
Vasa Recta which maintains the gradient
Normal Urine Components
- 95% water
- Urea
- Uric Acid
- Creatinine
- Ions- Na+, K+, Phosphate, Sulfate, Ca++. Mg++, bicarbonate
Abnormal Urine Components
Possible causes
-Glucose Diabetes Mellitus
- Proteins Renal Disease, High BP
- RBC Bleeding in urinary tract
- WBC Infection
- Bilirubin Liver Disease
- Ketone Bodies Diabetes, extreme diets
