Chapter 27-29 Flashcards
Excretion
What are the 4 primary functions?
What are the 4 primary organ systems?
- Control internal organic solute levels
- Control plasma water volume
- Remove non-useful and harmful substances
- Maintain osmotic balance
- Respiratory
- Digestive
- Integumentary (and glands)
- Renal
Excretion of Nitrogenous Wastes
What are the 3 different products of protein & nucleic acid catabolism?
- urea uric acid ammonia
Depend on water availability:
- Ammonia: ammonotelic animals
- In animals with lots of water-1 g : .5 L
- Urea: ureotelic animals
- Ammonium and bicarbonate are combined
- Less water – 1 g : .05L
- Uric acid: uricotelic animals
- Requires more ATP
- Less soluble, does not cause tonicity
- Removes more ammonium
- Requires less water 1g:.001L
Renal Organs
Protonephridia
Found in simple animals with one _____
examples?
- Cilia lower hydrostatic pressure in ducts
- Low pressure sucks small solutes out of flame cells
- Cilia force fluid and solutes out of body
internal fluid cavity
rotifers, flatworms, larva of annelids & mollusks
Renal Organs 2
Metanephridia
Found in simple animals with two or more fluid spaces
Examples?
Circulatory fluid is filtered into ___
Crustaceans, and adult annelids & mollusks
tubules
Renal Excretory Systems
What are the 4 jobs? 3 major ones.
- Filtration
- Secretion
- Reabsorption
- Osmoconcentration
- Mammals & birds
The Mammalian Kidney
Path of filtrate and urine
nephron
minor calyx
major calyx
renal pelvis
ureter
bladder
urethra
The ___ is the functional unit
nephron
The Mammalian Kidney: Urine Production
Urine production involves 3 main steps. What are they?
- Glomerular filtration (renal corpuscle)
- Tubular reabsorption
- Tubular secretion
Glomerular Filtration
The renal glomerulus is a unique ___ composed entirely of ___; therefore, it has a much ___ pressure than a normal capillary
Bowman’s capsule is ?
capillary network
arterioles
higher
the first part of the nephron, and is the site of collection of the initial glomerular ultrafiltrate
Glomerular Filtration 2
The glomerular capillaries are fenestrated to allow plasma and smaller compounds through while retaining blood cells and larger plasma proteins
Podocytes are ?
Filtration slits between the pedicels act like a sieve allowing the filtrate to enter the lumen of the nephron
cells in Bowman’s capsules which have multiple processes called pedicels
Regulation of Glomerular Blood Flow
maintained at a steady level by both intrinsic and extrinsic mechanisms:
Extrinsic: 2?
Intrinsic: 2?
- sympathetic nervous system – vasoconstriction of the afferent arteriole and a reduction in glomerular filtration
- hormones
- myogenic — smooth muscle of afferent arteriole; increase in blood pressure stretches the afferent arteriole causing reflex contraction which reduces the diameter and increases the resistance to flow.
- Juxtaglomerular apparatus – macula densa and granular cells
Juxtaglomerular Apparatus
Juxtaglomerular apparatus consists of:
Macula densa –?
Granular cells – ?
1. specialized tubule cells which monitor osmolarity and flow. If flow is high, vasoactive substances are released that constrict the afferent arteriole (may also do the reverse)
2. release renin which increases Na+ reabsorption in tubules via renin-angiotensin-aldosterone system
Tubular Reabsorption
99% of the glomerular filtrate is reabsorbed back into the bloodstream via the renal tubules
Different parts of the tubule have different properties regarding water and solute transport and permeability
Tubular Reabsorption: Proximal Convoluted Tubule
Apical microvilli on the epithelial cells of the proximal convoluted tubules increase surface area for the reabsorption of water and solutes
Tubular Reabsorption: Proximal Convoluted Tubule 2
In the proximal convoluted tubule, Na+ diffuses __ through the ___ membrane; and is pumped out ___ into the blood in the ___ membrane
Glucose and K+ are ___ cotransported with Na+ by a carrier protein in the apical membrane
A water channel allows reabsorption of water
- passively
- apical
- actively
- basolateral
- passively
Tubular Secretion: Distal Convoluted Tubule
K+ ions can be secreted by the cells of the distal convoluted tubule
Controlled by ___
aldosterone- secreted by the adrenal cortex
Tubular Secretion
Organic ions too large to get through the glomerular “sieve” are secreted by the tubule driven by the Na+ concentration gradient created by the Na+/K+ ATPase pump
Concentration of Urine
Urine-concentrating ability is due to what 2 major factors?
Maintaining an osmotic gradient between the renal cortex and the renal medulla
Varying the amount of water reabsorbed in the collecting ducts
Renal Corticomedullary Osmotic Gradient
Proportional to the length of the loop of Henle
What 2 major contributing factors?
- Varying permeability of renal tubule to different molecules in different areas (especially Na+ and urea)
- Countercurrent circulatory arrangement
Mechanisms of Renal Corticomedullary Osmotic Gradient
Two solutes are responsible for the corticomedullary concentration gradient. What are they?
- NaCl, which is actively pumped out of the tubule (1)
- Urea, which passively diffuses out of the tubule (3)
Countercurrent Multiplier Systems
In this countercurrent system, NaCl is ___ transported from the ___half of the loop to the __ half
Bulk flow concentrated the NaCl towards the U-turn
The mammalian kidney has a similar countercurrent arrangement in the loop of Henle
actively
bottom
top
Countercurrent Multiplier Systems
The countercurrent mechanism causes a large concentration gradient along the loop, but only a small concentration gradient across any point in the wall
This gradient is maintained by the arrangement of the capillary network surrounding the loop known as the vasa recta
Control of Water Reabsorption
Water reabsorption is controlled by a __ feedback system:
- Cells in the ___ respond to plasma osmolarity by secreting antidiuretic hormone (ADH/vasopressin)
- ADH increases water permeability in the collecting ducts
negative
hypothalamus
Urea becomes more concentrated in the fluid in the early portion of the collecting tubules as H2O is osmotically reabsorbed in the presence of vasopressin;
The urea cannot move out down its concentration gradient because this segment is impermeable to urea.
Urea does diffuse out of the late portion of the collecting tubule down its concentration gradient into the surrounding interstitial fluid and the nearby bottom of the long Henle’s loop, because these tubular segments are permeable to urea.
Vasopressin increases the permeability of the late collecting tubule to urea.
The entry of urea into the interstitial fluid contributes to medullary hypertonicity in the inner region of the medulla.
As the tubular fluid passes through the ascending limb and the distal tubule, urea cannot leave, because these segments are impermeable to it; thus the urea cannot diffuse out even though the fluid is passing through regions with lower concentrations of urea.
The tubular fluid’s urea concentration increases even further as water is reabsorbed when the fluid enters the early portion of the collecting tubule once again.
Thus, when vasopressin is secreted in the presence of a H2O deficit, this urea recycling progressively concentrates urea in the tubule fluid that is excreted as urine.
Vasopressin
Renin-Angiotensin
Renin-angiotensin-aldosterone system in a mammal. The kidneys secrete the hormone renin in response to reduced NaCl, ECF volume, and arterial blood pressure.
Renin activates angiotensinogen, a plasma protein produced by the liver, into angiotensin I.
Angiotensin I is converted into angiotensin II by angiotensin-converting enzyme (ACE) produced in the lungs.
Angiotensin II stimulates the adrenal cortex to secrete the hormone aldosterone, which stimulates Na+ reabsorption by the kidneys.
The resulting retention of Na+ exerts an osmotic effect that holds more H2O in the ECF.
Together, the conserved Na+ and H2O help correct the original stimuli that activated this hormonal system.
Angiotensin II also exerts other effects that help rectify the original stimuli.
Atrial Natiuretic Peptide
Atrial natriuretic peptide (mammal).
The atria secrete the hormone atrial natriuretic peptide (ANP) in response to being stretched by Na+ retention, expansion of the ECF volume, and increase in arterial blood pressure.
Atrial natriuretic peptide in turn promotes natriuretic, diuretic, and hypotensive effects to help correct the original stimuli that resulted in its release.
