BIOL 216 - Topic 4

Homeostasis

an internal condition maintained by internal responses that compensate for changes in the external environment, this is a dynamic condition

What makes homeostasis a dynamic condition

internal adjustments are constantly being made to counteract environmental changes to restore balance (stasis)

What are internal responses

the physiological processes of the body, carried out by the body systems in order to maintain the physical and chemical parameters that allow proper and efficient functioning of the body's component (cells, tissues, organs, and organ systems)

Why is homeostasis important

the internal environment must be maintained in such a state as to allow maximum efficiency

Examples of maximum efficiency importance

enzymes function best when within a certain range of temperature and pH, cells must maintain a balance between having too much or too little water in relation to their external environment

Cells are surrounded by

interstitial fluid

Interstitial fluid contains

ions (osmotic balance) and complex molecules (energy source)

Interstitial fluid is involved in

removal of wastes which is accomplished by the circulatory system in conjunction with the excretory system

Interstitial fluid (aka tissue fluid)

a solution that bathes and surrounds the cells of multicellular animals, the main component of the extracellular fluid (ECF) which also includes plasma

Plasma

the liquid component of blood

Examples of things that homeostatic mechanisms maintain

1. Concentration of oxygen and carbon dioxide, 2. pH of the internal environment, 3. Concentration of nutrients, waste products, salts and other electrolytes, 4. Volume and pressure of extracellular fluid

How does the body maintain homeostasis in general

by coordinating the activities of organ systems

The 11 organ systems are

nervous, endocrine, muscular, skeletal, integumentary, circulatory, lymphatic/immune, respiratory, digestive, excretory, reproductive

What does the body use to maintain proper gas composition during exercise

chemoreceptors

What does the body use to maintain proper blood pressure

baroreceptors

What does the body use to maintain water balance

osmoreceptors

What does the body use to balance pH

chemoreceptors

What does the body use for temperature regulation

thermoreceptors

How do the body systems contribute to homeostasis during exercise

muscles use more oxygen and produce more CO2, chemoreceptors sense the change from normal levels, intrinsic controls (vasodilators in this case) cause dilation of the blood vessels, allows more blood into those active areas of the muscles to bring in more O2 and take away CO2

Active hyperemia

increased blood flow through a tissue associated with increased metabolic activity

Vasodilator

chemical mediators that result in the dilation of blood vessels

Aspects of nitric oxide

vasodilator, freely diffuses through the plasma membrane and affects nearby cells, activates an enzyme that relaxes neighboring smooth muscle which dilates blood vessels thus increasing blood flow

When blood oxygen levels fall____in blood vessel walls synthesize and release ____

endothelial cells, nitric oxide

Endothelial cells are believed to be derived from the

mesoderm

Epithelial cells are derived from the

endoderm

Acetylcholine is released by

autonomic nerves in the walls of the blood vessel

Negative feedback mechanism path

stimulus, sensor, integrator, effector, response

Stimulus

environmental change

sensor/sensory receptor

specialized cells or neuronal endings that detect a change in factors such as pressure, temperature, pH, concentrations of molecules, etc, ex: free nerve ending in the skin

Integrator

control center that compares a variable to a set point and signals effectors to generate a response, ex: the brain

Effector

cell, tissue, or organ that responds to a signal from the control center and causes a change to reverse a situation and return the body to homeostasis, ex: a muscle or a gland

Response

the system's output

Negative feedback mechanism

the response of the system cancels or counteracts the effect of the original environmental change

Sensory transduction

stimulus (or change) is converted into an action potential

Action potential is ____along ___ towards the _____ where it is _____

transmitted, axons, central nervous system, integrated

Sensory transduction example

sensory cells (rods and cones) in the retina convert the physical energy of light signals into electrical impulses that travel to the brain

What are Baroreceptors

neurons (or neuronal endings) in the walls of the atria of the heart, the aortic arch, and the carotid sinuses, mechanical stretch receptors which generate electrical impulses (APs) when stretched, detect the amount of stretch in vessel walls, sensitive to changes in blood pressure, relay signals to the brainstem to elicit the appropriate response to restore homeostasis

Blood pressure

pressure exerted by the blood upon the walls of the blood vessels

What do baroreceptors do

send signals to the brainstem via the autonomic nervous system (involuntary: heart rate, digestion, respiration rate, etc) to elicit changes

What happens as you stand up and blood pressure falls

1. the baroreceptors are stretched less, 2. Rate firing APs to cardiac inhibitory centers decreases, 3. Cardiac output is increased which increases blood pressure thus restoring homeostasis

Chemoreceptors

in the aorta and carotid arteries, can detect O2 content in the blood

What happens when O2 content falls below normal levels/set point

1. Chemoreceptors send signals (APs) to the brainstem, 2. The brainstem integrates this information with the information from the baroreceptors, 3. Brainstem sends the signal to increase the rate and force of the heartbeat and respiration

What happens when the water levels in the body drop below set point

1. Osmoreceptors in the hypothalamus detect an increase in solute concentration in ECF due to water loss, 2. Hypothalamus stimulates thirst, 3. Water injection increases which compensates for the water loss, 4. Hypothalamus stimulates the posterior pituitary gland to secrete ADH, 5. ADH makes the distal convoluted tubules and collecting ducts permeable to water, the water is then reabsorbed, which reduces urinary output thus conserving water

ECF

extracellular fluids (plasma and interstitial fluid)

What are osmoreceptors

sense change in osmotic pressure

Osmotic pressure

the pressure that would have to be applied to a pure solvent to prevent it from passing into a given solution by osmosis, often used to express the concentration of the solution

What is affected when the osmotic pressure of blood changes

water diffusion into and out of the osmoreceptor cells

How are osmoreceptor cells related to the dilution of blood plasma

they expand when the blood plasma is more dilute and contract with higher concentration

What does the contraction or expansion of osmoreceptor cells do

causes an afferent neural signal to be sent to the hypothalamus which increases or decreases ADH secretion from the posterior pituitary gland to return blood concentration to normal levels

Hypertonic

solute concentration in solvent is higher than the concentration within the cells, draws water out of the cells, causes cell shrinkage

Isotonic

solute concentration is equal within and outside of the cells, even flow of water in and out of the cells

Hypotonic

solute concentration in solvent is lower than the concentration within the cells, cells draw water in, can cause cells to burst

What does the body use to maintain pH homeostasis

buffering systems, ex: CO2 + H2O

Ideal blood pH range

7.35-7.45

What might cause the plasma to be too acidic

respiratory, metabolic, or keto acidosis

Respiratory acidosis

decreased or obstructed respiration causes increased blood CO2 and decreased pH

Causes of respiratory acidosis

inability to ventilate adequately due to neuromuscular disease (ex: myasthenia gravis, amyotrophic lateral sclerosis), or COPD

COPD

chronic obstructive pulmonary disease, poor airflow as a result of breakdown of lung tissue or irritation of trachea and bronchioles leading to inflammation (largely caused by smoking)

Metabolic acidosis

can occur is the kidneys are not removing enough acid from the body

Nephron

functional unit of the kidney

Ketoacidosis

the body fails to adequately regulate ketones, often result of conditions such as Type 1 Diabetes and alcoholic ketoacidosis

Ketones

bi-products of fatty acid breakdown, ex: acetone, acetoacetic acid

How does Type 1 Diabetes result in ketones

lack of insulin-> no glucose absorption, so body switches to fatty acid metabolism-> ketones

How does alcoholic ketoacidosis result in ketones

alcohol blocks the first step of gluconeogenesis-> body doesn't synthesize enough glucose-> fatty acid metabolism-> ketones

How does accumulation of keto acids affect blood pH

they cause a decrease in blood pH

Why might the blood plasma be too basic

alkalosis which can occur as a result of hyperventilation

Hyperventilation

breathing really fast and deep after strenuous physical activity in an effort to get more oxygen for more energy causing the body to have a net loss of CO2 as more is being expelled than is produced in the body

What happens when the CO2 concentration of the blood falls ____its normal level

below, the blood's pH value is raised

How can CO2 levels be returned to normal post hyperventilation

breathing into a bag to rebreathe the exhaled air will result in a higher level of CO2 to be inhaled, resulting in the bloodstream levels to be replenished at a faster rate

Thermoregulation

maintaining temperature homeostasis for optimal efficiency

Animal cells can survive in a temperature range of

32-113 degrees Fahrenheit

How are cells affected by below freezing temperatures

the lipid bilayer changes from fluid to frozen gel, ice crystals form which disrupts cell function and destroys organelles

How are cells affected by high temperatures

proteins and nucleic acids unfold due to an increase in kinetic energy of molecules

Regulating body temperature within a range enables an animal to have

a high level of performance

Ectotherm

obtain heat from their environment, ex: some fish, invertebrates, amphibians

Aspects of ectotherms

must line in environment favorable to their body temperature requirements, typically have lower metabolic rate than endotherms, small surface to volume ratio enables them to retain more heat than endotherms, metabolic rate falls at low environmental temperatures which conserves energy

Endotherm

obtain heat from environment and can generate heat metabolically, ex: birds and mammals

Aspects of endotherms

maintain body temperature over a narrow range, balance internal heat production with heat loss from body surface, metabolic rate rises in low environmental temperatures which generates body heat

Torpor

period of inactivity aligned with variations in temperature, hibernation=winter, extivation=summer

Methods that animals use to change its conductance to heat

increase insulation, minimize heat uptake, redirect blood flow, counter-current flow for uninsulated parts

Methods of insulation

fluffing fur or feathers in colder temperatures to increase insulation (fur traps layer of air next to the skin which in turn traps heat lost thus insulating the body), blubber (layer of fat) works as an insulator for water creatures

Method of minimizing heat uptake

reflective surface on back to minimize warming from solar radiation (gazelle)

How is temperature regulated through the redirection of blood flow

at colder temperatures the blood can be directed to go further below the surface to insulate it and prevent heat loss, at warmer temperatures the opposite can occur to make it easier for heat to flow out of the body

Blood flow can be redirected by

vasodilation and vasoconstriction

Peripheral vasoconstriction

1. blood vessels in the skin constrict, 2. blood flow to the periphery is reduced, 3. Less heat is conducted from the blood through the skin to the environment, 4. Heat loss is reduced

If body temperature deviates from the set point

the hypothalamus triggers mechanisms that dilate or constrict blood vessels in the skin or vessels to the internal organs

You feel hot = temperature above set point, what happens

larger diameter of superficial vessels-> more blood flow-> more heat lost through skin

You feel cold = temperature below set point

larger diameter of internal vessels-> more blood flow to vital internal organs

Vasoconstriction ____ blood flow to an area, enabling ___ blood flow to another location

reduces, increased

How does counter-current flow for uninsulated parts work

1. Warm blood flows out to the uninsulated area, 2. Vessels are very close together causing the warm blood to lose heat to the cold blood returning to the main system, 3. Upon reaching the main system the cold return blood has been warmed, ex: limb of a bird that lives in the cold like a penguin or the flipper of a dolphin

Benefit of counter-current flow

ensures gradients that facilitate the maximal amount of heat retention, aka isolation of an uninsulated part of the body to prevent overall temperature changes resulting from movement of blood throughout the system

Counter-current flow vs concurrent flow

small gradients are maintained in the former and large gradients disappear quickly in the latter

In temperature regulation internal heat production is controlled by

negative feedback pathways, triggered by thermoreceptors and integrated by the hypothalamus

When temperature deviates from a set point in temperature regulation signals from receptors trigger

changes in blood flow to the body surface, sweating or panting, shivering, behavioral modifications

The four basic types of tissues

epithelial, connective, muscle, nervous

Epithelial tissue

lines body structures and cavities, forms protective, secretory, and absorptive coverings, "protection, transport, secretion, and absorption"

Connective tissue

structural support

Muscle tissue

movement

Nervous tissue

transmits information, "communication, coordination, and control"

Three common shapes of epithelial cells

squamous, cuboidal, columnar