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BIOL370 Study Guide - Final Guide: Active Transport, Blood Vessel, Respiratory System

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Dinu Nesan
Study Guide

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Lecture 7: The Kidney
- Transporter expression in epithelial cells controls solute uptake & deposition
- Length of the loop is directly related to urine concentration
- Single effect based on active NaCl transport
- Countercurrent multiplication is a key to producing concentrated urine
- Endocrine regulation of urine formation
- Internal organ with multiple cell types “tubule” that maintains ion & water balance
- Vertebrate kidney (6 roles in homeostasis)
o Ion balance: Na+
o Osmotic balance: Urine volume
o Blood pressure: Long term regulator
o pH balance: w/ Respiratory system [H+ vs. HCO3
o Excretion of metabolic wastes & toxins
o Hormone production: Renin that controls BP & Erythropoietin that regulates RBC synthesis
- Mammalian kidney (Filtration Reabsorption Secretion Excretion)
o Outer cortex + Inner medulla
o Kidney Ureter Urinary bladder Urethra
o Functional unit of the kidney: Nephron
Renal tubule: 1 layer of transport epithelium with specific transport functions @ different
Associated vasculature “blood vessels”: Glomerulus surrounded by Bowman’s capsule &
capillary beds that surrounds the renal tubule
o Cortical Nephrons: Loop of Henle is located predominately @ outer cortex
Peritubular capillaries are efferent arterioles that drains the cortical nephrons
o Juxtamedullary Nephrons: Loop of Henle is located deep into the inner medulla
Vasa recta are efferent arterioles that drains the juxtaglometular nephrons
- Function of the Kidney
o Urine formation
Primary urine (introduced into the kidney via ultrafiltration) Definitive urine (solution
before elimination)
Ultrafiltration: Pressure driven mass flow
o Filtration of blood at the glomerulus
Water & small solutes crosses the glomerular wall through filtration slits
Blood cells & large macromolecules are not filtered/retained
Fenestrated glomerular capillaries are lined with podocytes (with pedicles)
Mesangial cells in-between capillaries with podocytes to control blood pressure &
filtration within glomerulus, they can initiate contraction to restrict blood flow
Glomerular Filtration Rate (GFR): The amount of filtrate production per minute @
Determined by balance of pressures across the glomerular wall (3)
o Glomerular capillary hydrostatic pressure (60mm Hg)
o Bowman’s capsule hydrostatic pressure (15mm Hg)
o Oncotic pressure (30mm Hg): Osmotic pressure due to protein in blood
GFR = 15mm Hg
Intrinsic Regulation of GFR (3)
Myogenic regulation: Autocrine regulated, constriction/dilation of afferent arteriole
o ↑GFR ↑ Filtration pressure ↑Capillary pressure ↑ Afferent
arteriolar pressure Arteriole SM stretches ↑ Constriction of afferent
tubule ↓ GFR
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Tubuloglomerular feedback @ Juxtaglomerular apparatus
o Macula densa cells in the distal tubule can signal Juxtaglomerular cells in the
afferent arteriole to control the diameter of the afferent arteriole
o ↑ GFR ↑ Filtration pressure Capillary pressure ↑ Flow @ macula
densa of distal tubule Chemical signal release ↑ Constriction of
afferent tubule Capillary pressure
Mesangial control: Changes in filtration apparatus to alter the permeability of the
Extrinsic Regulation of GFR (3 hormones)
Vasopressin: Antidiuretic to ↓ Loss of H2O
Renin-Angiotensin Aldosterone pathway: Increases Salt retention, ↓ H2O loss
Atrial Natriuretic peptide: Increases GFR
Filtrate flows from the Bowman’s capsule into the proximal tubule
o Reabsorption where specific molecules in the filtrate are removed back to the blood
Most water & salt is reabsorbed using transport proteins & energy
Renal threshold: The rate of reabsorption is limited by the # of transporters
o Concentration of specific solute can overwhelm re-absorptive capacity
Most reabsorption, and some secretion takes place at the proximal tubule
Na+ cotransporter with inorganic or organic molecules
Water then follows by osmosis
Major driving force: Na+/K+ ATPase @ basolateral membrane (Primary transporter)
E.g. Glucose reabsorption via secondary active transport
o Basolateral Na+/K+ ATPase pumps out Na+ (favorable inward Na+ gradient) @
apical side
o Apical: Na+/Glucose cotransporter (Secondary transporter) & Na+/H+
exchanger brings Na+ & glucose into the cells
o Basolateral: Glucose permease allows glucose to cross via facilitated diffusion
o Secretion of specific molecules into the filtrate
Molecules that are secreted include K+, NH4
+, H+, pharmaceuticles etc.
Loop of Henle: Descending (H2O reabsorption) & Ascending (Solute reabsorption)
Descending limb: Permeable to water (aquaporin)
o Water is reabsorbed & primary urine becomes more concentrated
o 300mOsM 1200mOsM
o H2O enters from the apical side via osmosis
Ascending limb: Impermeable to water (no aquaporin)
o Ion are reabsorbed & primary urine becomes dilute
o Apical NKCC, K+ secreted @ apical side
o Basolateral Na+/K+ ATPase excretes Na, Cl-/K+ cotransporter excretes Cl- & K+,
Cl- channel excretes Cl-
o 1200 mOsM 100 mOsM
Distal tubule: Reabsorption completed
Hormone mediated regulation of solutes & water uptake, alters the level & activities
of transport proteins
o Adrenal gland cortex: mineralocorticoid
o Hypothalamic-pituitary: vasopressin
o Parathyroid: Parathyroid hormone
Apical: Na+-Cl- cotransporter takes both in, Na+ is excreted @ basolateral side via
Na+/K+ ATPase & Cl- leaves @ basolateral side via Cl- channels, K+ is secreted
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