Bio Gr 12: Homeostasis

Chapter 9

9.1- Maintaining an Internal Balance

Homeostasis

• physiological state where physical and chemical conditions in a living organism remain in a constant range, suitable for life processes

• not a goal, or result, but something that is constantly maintained, adjusting conditions based on a multitude of factors

• we do not always want to be at homeostasis, but we want to be close to it (in order to reach true homeostasis, we would need to be dead)

• homeostasis differs for different activities (running, sleeping, etc.)

• some conditions are very tolerant to change, others are more broad: fluid volume, pH, pressure, osmotic flow, solute concentration, hormone level, temperature, etc. (small changes in these can be fatal)

Internal Environment

• extracellular fluid (ECF) that surrounds cells in the body

• includes interstitial fluid (between the cells and blood plasma)

• these fluids ensure the health and proper functioning of cells, and therefore the proper functioning of tissues, organs, and organisms

Systems

• circulatory and lymphatic systems: transports essential materials throughout the body and aids in the immune response

• digestive, respiratory , excretory system: add nutrients and remove waste from blood, tissues and body, moves dissolved gasses

• muscular and skeletal system: allows for movement and provides protection to internal organs

• reproductive system: produces and transports gametes

• nervous and endocrine systems: coordinate and regulate the function of the body's systems, often response to the environment

• these systems work together to maintain dynamic equilibrium

• equilibrium is not a set state, it changes depending on influencing factors, meaning it is a dynamic equilibrium (we want this)

9.2- Homeostasis and Feedback Mechanisms

Feedback Mechanisms

• there are 3 components:

• the sensor: tissue that gathers information that will detect a change in the environment or a stimulus, which is then passed on to the integrator

• the integrator: processes information from the sensor and compares it to a set of established, ideal conditions

• these ideal conditions are referred to as set points (not set, they can also change dynamically)

• when the environment imposes conditions that fall outside the set points, the integrator activates the effector

• the effector: the components of a system that work to return the system to the established set points. It can also affect behaviour (you're cold one day, so the next you wear an extra layer)

• sensors and integrators tend to belong to the endocrine or nervous systems, while effectors can vary in tissue types

Negative Feedback Mechanisms

• an organism reacts in order to compensate for changes made so that it may maintain its state of equilibrium

• they act oppositely to the effect of how the stimulus is trying to change the system

• like shivering, sweating, vasoconstriction, vasodilation for temperature fluctuation

• if it is cold outside, this works to oppose that change and keep you warm

Positive Feedback Mechanisms

• acts to enhance or increase the condition that led to the change in the system

• since it enhancing an external characteristic, positive feedback does not restore equilibrium, but the work to exaggerate the imbalance

• like blood clotting, breast feeding, fever

• these changes are usually temporary, and work with a larger system to eventually allow for homeostasis to recur

9.3- Thermoregulation

Thermoregulation

• process in which the body regulates its internal temperature

• thermoreceptors (special sensors), detect variation in body temperature

• when they detect a large enough variation, they initiate actions to adjust it

• this can be done by fluctuating the rate of metabolic reactions, or adjusting the amount of thermal energy absorbed or released through the body surface

Modes of Exchange

• exchange will occur at the surface of the body in 4 ways

  1. conduction: thermal exchange through direct contact between particles

  2. radiation: transfer of energy through the emission of EMR (electromagnetic radiation)

  3. convection: transfer of energy through fluids

     • a fan works because it removes warm air particles from beside you, replacing them with colder ones, but it does not actually cool the room

  4. evaporation: liquid evaporates off the body surface, hence cooling it

• energy in must equal energy out, in order to maintain equilibrium

Types of Regulators

• all animals are either:

• homeotherms, where the body temperature stays constant regardless of environment conditions, maintaining the internal temperature through internal physiological mechanisms that generate heat (endothermy, endotherms) (mammals)

• Poikilotherms, where the body temperature changed with, and usually matches the external environment, and will alter their behaviour and association with he environment to regulate their temperature (ectothermy, ectotherms) (reptiles)

Ectotherms

• invertebrates, fish, reptiles, amphibians

• some organisms will move to warmer areas, or others will seek shelter to move away from the sun, all in order to maintain their metabolic rates and output

• ectotherms also use physiological responses:

• some will modulate blood flow to or away from body surface

• some will change their physiology seasonally so they can tolerate colder temperatures in winter and warmer in summer (thermal acclimatization)

Endotherms

• metabolic processes will fuel the heat generated in mammals

• cells have more, larger mitochondria than ectotherms

• many strategies to maintain heat:

• if too cold- vasoconstriction, shivering, raised hair

• if too hot- vasodilation, sweating, panting

• behavioural changes for both

Other Endotherm Responses

• Torpor: a short term method of lowering energy demand, by dropping the metabolic rate, letting the temperature drop below usual temperatures

• Hibernation: longer term state of torpor due to seasonal changes, induced by shorter days and colder temperatures

• estivation: summer torpor caused by heat or drought (plants do this a lot)

9.4- Water Balance

Osmosis

• osmotic pressure: fluid pressure resulting from different in water concentration gradient across a permeable membrane (water moves towards more solute)

• the greater the difference, the greater the pressure

• Hyperosmotic (hypertonic): the side of system that has the higher solute/ lower water concentration, water moves towards

• Hypoosmotic (hypotonic): the side of system that has the lower solute/ higher water concentration, moves away

• Isoosmotic (isotonic): same solute/ water concentration on both sides, water moves across at an equal rate in both directions

• Hydrostatic pressure: pressure can influence water flow irrespective of osmotic state

Excretion (Urinary System)

• to maintain homeostasis our bodies must be able to get rid of toxic, metabolic products

• excretion of liquid waste removes nitrogen compounds

• aqueous environment of the body acts as a solvent for wastes

• the excretion of waste allows for proper osmoregulation, pH and ion balance

• also very important for water retention, especially for terrestrial animals

Urinary

• urinary system takes waste molecules metabolised by the liver so they are soluble in water and facilitates their removal

• main organs include:

• kidney: produces urine

• bladder: stores urine

• ureter: tube that connects kidney to bladder

• urethra: tube that carries urine from bladder to environment

• cortex: outer layer of kidney

• medulla: inner layer of the kidney

• renal pelvis: where the kidney and ureter join

9.5- Excretory System

The Human Excretory System

• humans and most vertebrates excrete wastes through the lungs, intestines and kidney

• The goal of the kidney is to excrete nitrogenous wastes

• the kidney is made up of millions of functional units called nephrons, accumulation of different tissues

• nephrons filter blood, coordinate excretion, maintain blood pH and maintain osmotic balance

Kidney

• humans have 2 kidneys, one on each side of the spine (it is possible to have 2 kidneys on one side, rare, but possible)

• waste filled blood is sent in via the renal artery, and clean, filtered blood is sent out from the renal vein

• the kidney has visible inner and outer layer, the outer layer is called the renal cortex, the inner layer is called the renal medulla

• there is an opening in the renal pelvis that connects to the ureter—> bladder—> urethra—> excretion

Nephrons

• made of several components:

• Glomerulus: high pressure capillary bed where filtration begins

• afferent arteriole: small arterial branches that bring blood to the glomerulus

• efferent arteriole: small arterial branches that bring blood away from the glomerulus

• bowman's capsule: cuplike ending of a tubule that surrounds the glomerulus

• proximal tubule: a duct that connects the bowman's capsule with the loop of henle

• loop of henle: a U- shaped part of the duct that connects the proximal tubule to the distal tubule

• distile tubuule: connects the loop of henle to the collecting duct

• peritubular capillaries: network of blood vessels that surround the nephron

Urine Formation

1. filtration

2. reabsorption

3. secretion

• urine is hypoosmotic, in order to ensure water efficiency, water will need to constantly move into the body tissue from the urine (ONLY WATER, NOT WASTES)

• nephrons have 3 features allowing for this: the arrangement of the components, changes in permeability of the nephric parts, and the change in concentration of solute in interstitual fluid of the kidney

Filtration

• blood moves through the afferent arteriole into the glomerulus

• the membranes of the glomerulus and the Bowman's Capsule make a semi permeable filter

• the blood in the glomerulus is under high hydrostatic pressure, forcing the fluid part of blood into the Bowman's Capsule

• the filter size is large enough to let in small molecules (water, ions, glucose, AAs, nitrogen)

Reabsorption

• all the solute that it not nitrogenous waste needs to be taken back in to the body tissue

• the fluid in Bowman's Capsule enters the proximal tubule where the reabsorption begins

• through active and passive transport, ions K, Na, Cl (through pump proteins), AAs, and sugars will leave the filtrate in the proximal tubule for the surrounding fluids

• the water in the tubule is hypoosmotic and will follow the solutes into the surrounding tissue

• all outward flow is facilitated by microvilli in the tubule to increase surface area but water in particular travels at an even greater rate because of water channel proteins called aquaporins

• H+ will also move in actively from the blood, raising blood pH

• the urea rich fluid flows into the descending loop of Henle where water and ions will be forced out passively and actively

• this further concentrates the waste in the urine

• the ascending loop of henle has too high a solute concentration to passively let water and ions out, it is actively transported out from the top of the loop

• urine is increasingly concentrated and water volume is removed—> less to filter, more efficient

• the urine then enters the distal tubule where the process repeats (leak ions, water, take H+, concentrate waste further)

• urine moves to the collection ducts

• collection ducts are only permeable to water and urine concentrates further

• near the bottom of the collecting duct there are passive urea channels that allow urea to leak out

• this establishes a more favourable osmotic gradient outward and facilitates further removal of water here

Secretion

• waste are concentrated in the tubules 4 times more than when they entered

• the urine travels through the urinary tract until the bladder is excreted through the urethra

• H+ is secreted into the distal tubule to help with pH balance

• K+ is secreted into the tubule to help with osmotic balance

Diseases

• diabetes mellitus

• malfunctions of the pancreas or insulin mechanisms causes blood sugar content to rise

• causes the sugar content in the nephron to remain high despite the work of active transport to remove solutes from the nephron

• this makes the nephron retain water and more frequent urination is common, leads to dehydration and feelings of chronic thirst

• can be detected by urinalysis testing, usually elevates levels of sugar in the urine

• diabetes insipidus, totally different, leads to the same outcome as above

Kidney Stones

• dissolved ions (phosphates and carbonates) will combine with calcium ions to form insoluble precipitates

• these can grow into large and jagged stones which can lodge in the renal pelvis, ureter, and urethra

• very painful, especially in males since our tubes tend to be wider, so more space, females do not feel it as much

• treated by ultrasound, uteroscopic or surgical removal

Kidney Failure

• total loss of kidney function can require the use of dialysis machine

• dialysis is the process of mechanically filtering the blood, instead of the kidney

• kidney transplant required

Chapter Quiz:

• kidney anatomy

• filtration, reabsorption, secretion