BSC-2010 Lecture Notes - Lecture 12: Proximal Tubule, Osmotic Concentration, Cell Nucleus

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2 Dec 2016

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Regulating the Internal Environment Part 1: Bioenergetics and Regulation of Body Temperature
Bioenergetics — energy flow and transformation in an animal
(1) Organic molecules in food
(2) Digestion and absorption
Heat released
Energy lose in feces
(3) Nutrient molecules in body cells
Carbon skeletons formed
Cellular respiration
Heat is released
ATP allows for cellular work
Allows for biosynthesis
This is a cycle, it continues
Basal (resting) metabolic rate (BMR) of mammals increases with body sized
Larger animals have more cells and tissue = greater O2 consumption
Basal metabolic rate (BMR) PER UNIT O FMASS decreases with body size of mammals
Individual cells of small animals consume more O2 per hour
Homeostasis (maintaining a constant internal environment): Temperature Regulation
The relationship between body temperature and environmental temperature in an
aquatic endotherm and ectotherm
River otter - temperature regulator
Largemouth bass - temperature conformer
A nonliving example of negative feedback: control of room temperature
Thermostat turns heater o
Room temperature decreases
Room temp. at 20 degrees C, set point
Room temperature decreases
Thermostat turns heater on
Room temperature increases
Room temperature at 20 C
Room temp. increases
Then the process begins again
Heat exchange between n organism and its environment
Hypothalamus acts as a thermostat in humans
Thermostat in hypothalamus activates cooling mechanisms
Body temperature increases
Blood vessels in skin dilate
Body temperature decreases
Normal body temp
Body temperature continues to decrease
Thermostat in hypothalamus activates warming mechanisms
Blood vessels in skin constrict
Body temperature increases
The cycle continues
Human Circadian Clock: daily variations in core boyd temperature and melatonin (a
Melatonin is a hormone that is secreted by the pineal gland (brain)
Melatonin is a modified amino acid (it is an amine)
Insulation by adipose tissue: Evolutionary adaptation that reduces heat loss by
conduction/ convection
Walrus - an endotherm
Countercurrent heat exchangers: Evolutionary adaptation that keeps heat in the body
Minimizes heat loss by conduction/convection at extremities
Regulating the Internal Environment Part 2: Extracellular Fluid Composition - Osmoregulation and
Osmoregulation in a freshwater fish
Gain of water and some ions in food
Uptake of salt ions by gills
Osmotic water grain through gills and other parts of body surface
Excretion of salt ions and large amounts of water in dilute urine from kidneys
Lake water is hypoostmotic to body fluids of most freshwater fish
Osmoregulation in a marine fish
Gain of water and salt ions from food
Gain of water and salt ions from drinking seawater
Excretion of salt ions from gills
Excretion fo salt ions and small amounts of water in scanty urine from kidneys
Osmotic water loss through gills and other parts of body surface
Seawater is hyper osmotic to body fluids of most saltwater fish
Forms of Nitrogenous Waste
Proteins // Nucleic Acids
Amino Acids // Nitrogenous bases
NH2 Amino Groups
Most aquatic animals, including most bony fishes
Forms ammonia, toxic!
Mammals, most amphibians, sharks, some bony fishes
Many reptiles (including birds) insects, and land snails
Uric acid
Urea & uric acid:
Less toxic than NH3 but more complex molecules tame more energy (ATP) to
Key Steps of Excretory System Function: An Overview
(1) Filtration
Filtrate goes through the excretory tubule
(2) Reabsorption
(3) Secretion
(4) Excretion
Comes out as urine
What are the major, homeostatic functions of the human kidney?
Water (blood plasma) volume
Hydration state: balance water gain and loss
Total solute concentration
Reabsorb/excrete specific solutes
Electrolyte (and other small solute) concentrations
Reabsorb/excrete Na+, K+, Cl-, Ca2+
Excrete nitrogenous wastes (from protein and nucleic acid metabolism)
From ruin (water, urea…)
The Mammalian Excretory System
Nephron (functional unit)
Look at the anatomy…
Nephron and collecting duct: Regional Functions of the Transport Epithelium
(1) Proximal tubule
(2) Descending limb of loop of Henle
(3) Thin segment of ascending limb — thick segment of ascending limb
(4) Distal tubule
(5) Collecting duct
How the Human Kidney Concentrates Urine: The Two-Solute Model
Includes both active and passive transport
Has dierent selective permeabilities
Hormonal Control of the Kidney by Negative Feedback Circuits: ADH
Osmoreceptors in hypothalamus trigger release of ADH
ADH (a peptide hormone) enhances fluid retention by increasing re-uptake of
water by kidneys
Also increases thirst
Hypothalamus generates thirst
Drinking of water
Normal blood osmolarity
Blood osmolarity increases
Hormonal Control of the Kidney by Negative Feedback Circuits: RAAS
Renin-angiotensin-aldosterone system (RAAS) maintains blood volume and increases
blood pressure
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