Chapter 48: Osmoregulation, Excretion, & Thermoregulation (Urinary)

Summarize the mechanisms cells use to exchange water and solutes with the surrounding fluid

Osmosis and transport mechanisms.

Describe the structure and function of excretory tubules

Tubular structures involved in filtering body fluids and excreting waste products.

Compare and contrast the solubility and toxicity of the nitrogen compounds in metabolic wastes

Ammonia is highly toxic and soluble. Urea is less toxic and soluble. Uric acid is least toxic and insoluble.

Summarize osmoregulation and excretion processes in invertebrates

Invertebrates use various structures like protonephridia and metanephridia for osmoregulation and excretion.

Describe the components of the mammalian urinary system

Kidneys, ureters, urinary bladder, and urethra.

Discuss the processes of filtration, reabsorption, and secretion in the mammalian kidney

Filtration occurs in the glomerulus, reabsorption returns essential substances to the blood, and secretion moves additional wastes into the filtrate.

Describe the systems that regulate mammalian kidney function

Hormonal systems (e.g., RAAS, ADH) and local controls.

Compare and contrast kidney function in nonmammalian vertebrates

Kidney function varies among nonmammalian vertebrates depending on their environment and physiology.

Compare and contrast ectothermy and endothermy

Ectotherms obtain heat primarily from the external environment; endotherms generate most of their heat internally.

What is a hyperosmotic solution?

A solution with higher osmolarity.

What is a hypoosmotic solution?

A solution with lower osmolarity.

What is an isosmotic solution?

Solutions on either side of a membrane have the same osmolarity.

Ammonia

NH3, result of biochemical steps.

Renal cortex

Pale outer region of the kidney.

Renal medulla

Darker central region of the kidney.

Renal artery

Carries blood into the kidneys.

Renal vein

Filtered blood leaves the kidney by the renal vein.

Urine pathway

Collecting ducts → renal pelvis → ureter → urinary bladder → urethra.

Daily filtration in humans

Bowman’s capsule filters 180L of fluid each day from 1,400L of blood.

Major calyces

Funnel-like structures formed from minor calyces, forming the ureter within a kidney.

Minor calyces

Form major calyces and act as collecting cups for urine, fitting over renal pyramids.

Renal pyramids

Cone-shaped renal tissue in the medulla containing tubules that transport urine to the calyces.

Efferent arteriole

Formed from capillaries after the glomerulus.

Peritubular capillaries

Formed by the efferent arteriole, surrounding the renal tubules before returning to the venous system.

Glomerulus

A group of anastomosing capillaries (glomerular tuft) in the nephron, invested by Bowman’s capsule.

Bowman’s capsule

Double layer of epithelial cells investing the glomerulus.

Filtration unit of the nephron

The whole glomerulus.

Bowman’s capsule components

Visceral epithelial cells (podocytes and filtration slits) and parietal epithelial cells.

Afferent arteriole (A)

Carries blood to the glomerulus.

Efferent arteriole (B)

Carries blood away from the glomerulus.

Glomerular capillaries (C)

Capillaries within Bowman's capsule where filtration occurs.

Bowman’s capsule (D)

Cups around the glomerulus to collect filtrate.

Endothelium (E)

The lining of the glomerular capillaries.

Distal convoluted tubule (F)

Part of the nephron tubule after the loop of Henle.

Urine formation processes

Glomerular filtration, selective reabsorption, tubular secretion.

Nephron

Functional unit of the kidney (~1.2 million per human kidney).

Glomerular filtration location

Occurs in Bowman’s capsule around the glomerulus.

Ultrafiltrate of plasma

Produced by the glomerulus.

Podocytes

Visceral epithelial cells of Bowman’s capsule, forming filtration slits with glomerular endothelial cells and basement membrane.

Filtration slits

Formed by podocyte foot processes and glomerular endothelial cells, allowing filtration.

Diameter difference in arterioles

Diameter of afferent arteriole > efferent arteriole.

Reabsorption in the PCT (Proximal Convoluted Tube)

Reabsorption of water, ions, and nutrients into the interstitial fluid.

Na+/K+ pumps in PCT

Move Na+ and K+ from the filtrate into the interstitial fluid.

Cl– ion reabsorption in PCT

Reabsorbed from the tubule with positive ions due to a voltage gradient.

Reabsorption of glucose and amino acids in PCT

Via specific active transport proteins.

Renin

Enzyme that cleaves angiotensinogen to angiotensin I.

Angiotensinogen

Precursor protein cleaved by renin.

Angiotensin I

Decapeptide formed from angiotensinogen.

Angiotensin Converting Enzyme

Converts angiotensin I to angiotensin II.

Osmoregulation in terrestrial amphibians

Conserve water and salt. Salt reclaimed in the bladder by active transport.

Ectotherms

"Cold-blooded" animals obtaining heat primarily from the external environment.

Endotherms

"Warm-blooded" animals obtaining most of their heat from internal physiological sources.

Ectotherm thermoregulation

Regulate body temperature by controlling heat exchange with the environment through behavior and physiology.

Endotherm thermoregulation

Keep bodies at optimal temperature by regulating heat generated internally and heat loss.

Temperature-regulating mechanisms

Metabolic heat production, heat loss by evaporation (vasoconstriction or vasodilation), shivering.

Response to cold (hypothalamus)

Hypothalamus sends signals to trigger compensating mechanisms via the autonomic nervous system.

In animals with a circulatory system, the ECF includes both ___ and _____ _____.

Interstitial fluid and blood plasma

_ is the diffusion of water across a membrane

Osmosis

The total solute concentration of a solution is called its , and it is measured in

Osmolarity, Osmoles

A solution with a higher osmolarity is ____osmotic to the other solution

Hyperosmotic

A solution with lower osmolarity is ____osmotic to the other solution

Hypoosmotic

What is the difference between an osmoconformer and an osmoregulator?

Osmoconformer - match the osmolarity of environment; Osmoregulator - Control osmolarity independent of the environment

Give the 4 key steps of Excretory System function? (in correct order)

Filtration, Reabsorption, Secretion, Excretion

What are nitrogenous products broken down and excreted as? (give all 3 options)

Ammonia, Urea, Uric Acid

• Give an example of an organism that excretes each waste product

Ammonia - aquatic animals; Urea - mammals; Uric Acid - birds, reptiles

The ___ ____ is the body’s way of converting toxic ammonia into urea

Urea Cycle

1. Core temperature

Set point temperature that is subjected to homeostatic regulation

2. Thermoreceptors

Receptors that detect changes in body temperature, crucial for thermoregulation

3. Ectotherms, external environment

Ectotherms primarily obtain heat from the external environment

4. Endotherms, internal physiological sources/biochemical reactions

Endotherms maintain their body temperature internally independent of the environment by regulating two main processes: the amount of heat generated by internal oxidative reactions and the amount of heat exchanged with the environment

5. As environmental temperature falls, the ectotherms metabolic rate _________, while the endotherms metabolism ___________

decreases, increases

6. The two types of thermoreceptors are and _ thermoreceptors.

Peripheral, central

1. List the methods of heat exchange and describe them.

Radiation - emission of electromagnetic energy; Evaporation - heat loss through vaporization of liquid; Convection - transfer of heat by movement of air or liquid; Conduction - direct transfer of thermal energy between objects in contact.

2. What are the activity and food-intake changes in endotherms vs ectotherms at low temperatures?

Endotherms - increase metabolic rate and food intake to generate heat; Ectotherms - decrease activity and food intake due to lowered metabolic rate.

3. Describe how endotherms vs ectotherms regulate their body temperature

Endotherms - regulate internal heat production and heat loss through physiological mechanisms; Ectotherms - regulate body temperature through behavioral and physiological mechanisms of heat exchange with the environment.

1. The metabolic rate of endotherms is always higher than that of ectotherms of the same size

True

2. An ectotherm uses more energy in the cold than in the warm

False

3. There is a characteristic circadian fluctuation of about 1°C with temperature being highest during the night and lowest during the day

False, temperature is highest during the day and lowest during the night

Osmoregulation

Regulation of water and ion balance.

Role of excretory tubule in osmoregulation

Excretion of fluids and solutes maintains the body’s water and ion balance.

Importance of osmoregulation

Maintaining metabolic and biochemical reactions and transport of nutrients.

Thermoregulation

Homeostatic maintenance of body’s temperature.

Osmolarity units

osmoles/L.

Total solute concentration of body fluids

300 osmol/L.

Intravascular osmolarity

Tends to be higher due to plasma proteins.

Osmosis definition

Movement of water from a region of higher water concentration to a region of lower water concentration through a semipermeable membrane.

Hyperosmotic (AKA hypertonic)

Higher solute concentration Outside of Cell

Hypoosmotic (AKA hypotonic)

Lower solute concentration outside of cell

Isosmotic (AKA isotonic)

Equal solute concentration.

Osmoconformers

Osmolarity matches with the environment.

Osmoregulators

Control osmolarity independent of the environment.

Nephron definition

Structural and functional unit of the kidney.

Renal corpuscle

Bowman's capsule and glomerular capillaries.

Renal tubule

Extends from Bowman's capsule and includes the PCT, loop of Henle, DCT, and collecting duct.

Average number of nephrons per adult kidney

~1.2 million.

Components of the nephron

Bowman’s capsule, glomerular capillaries, proximal convoluted tubule, descending thin limb of the loop of Henle, loop of Henle, ascending thin limb of the loop of Henle, ascending thick limb, distal convoluted tubule, connecting tubule, collecting duct.

Cortical nephrons

Located in the outer part of the cortex.

Juxtamedullary nephrons

Located along the base of the renal medullary pyramids.

Glomerular filtration

Occurs in Bowman’s capsule; driving force is hydrostatic blood pressure.

Glomerulus structure

Anastomosing network of blood capillaries.