Chapter 15: Bio Homeostasis

Feedback control maintains

the internal environment of many animals

Multicellularity allows for

cellular specialization

Specialization requires organization and maintenance of

internal environments different from external

Homeostasis

maintains a “steady state” or balance internally regardless of external environment

Body temperature, blood pH, glucose concentration, Relies on negative feedback

Regulator

Use internal mechanisms to control internal change despite external fluctuations

Maintain internal body temperature even when external environment is hot/cold

Conformer

Allow internal condition to change in response to external changes

Body temperature changes as external environment changes

Endocrine System

A collection of glands that produce hormones that influence almost every cell, tissue, organ, and function in the body

Pineal gland

Melatonin

Thyroid gland

Thyroid hormone (T 3 and T 4)

Parathyroid glands

Parathyroid hormone (PTH)

Ovaries (in females)

Estrogens and Progestins

Testes

Androgens

Posterior pituitary

Oxytocin Vasopressin (antidiuretic hormone, ADH)

Pancreas

Insulin and Glucagon

Adrenal cortex

Glucocorticoids and Mineralocorticoids

Adrenal medulla

Epinephrine and norepinephrine

Negative Feedback

Response reduces stimulus and promotes a negative feedback

Positive Feedback

Response increases stimulus and promotes a positive feedback

Simple Endocrine Pathways

1. Digestive juices in the stomach are extremely acidic

2. must be neutralized before the next steps of digestion

3. Coordination of pH control in the duodenum relies on endocrine pathway (using neg feedback)

Neuroendocrine Pathways

1. Hormone pathways that respond to stimuli from

external environment (Rely on sensor in nervous system)

2. Hypothalamus integrates endocrine and nervous systems

3. Signals travel to pituitary gland (Via positive feedback)

Many hormones elicit more than

one type of response (Depends on cell type and location)

Epinephrine

ssecreted by adrenal glands → increases blood glucose and flow to muscles and decreases blood flow to digestion

Juvenile hormone

regulates behavior and development in butterflies

Thyroid hormone plays key role

in metabolism across many different animals

Osmoregulation

Process of animals controlling solute concentration in interstitial fluids (balance if water gains and losses)

Osmolarity

Solute concentration of a solution ( Isotonic, hypotonic, hypertonic )

Freshwater Fish

Live in hypotonic environment

• Prevent salt loss

• Scaled, mucus-covered

• Nearly waterproof

• Water enters by osmosis across gills

• Pumped out by kidney

• Actively absorb NaCl across gills

• Salt present in food replaces any lost

Marine Fish

Live in hypertonic environment

• Actively drink seawater

• Drink enough to replace water lost

• Salt absorbed in intestines

• Salt carried by blood to gills

• Secreted by gills

• Ions remain are voided with feces

• Maintain body fluids at low concentration (1/3 of seawater)

Nitrogenous Waste

Breaking down proteins and nucleic acids result in nitrogenous molecules

Protonephridia

Flatworms/ Networks of dead-end tubules connected to external openings

Malpighian tubules

Terrestrial arthropods and Diffuses without filtration

Vertebrates have kidneys that function in both

osmoregulation and excretion

Vertebrate Excretory System

Remove nitrogenous waste

Regulate salt and water concentrations

Large blood vessels

Filtration

Filtering body fluids via physical force

Reabsorption

Reclaiming valuable solutes

Secretion

Adding nonessential solutes, wastes

Excretion

Releasing processed solution from body

Enzymes have an

optimum temperature

Ectothermy

heat is conducted away as quickly as it’s produced

Must still maintain homeostatic temperature at given points in time

Must still maintain homeostatic temperature at given points in time

Endothermy

generate enough heat to maintain stability

Must maintain temperature

Much of daily caloric intake goes to generating heat

• Must eat more than ectotherms

Heat is lost through radiation, conduction, and convection to cooler environment

• And by evaporation

Heat is increased in cold temperatures via

• Shivering

• Increasing insulation

Metabolic adjustments (ectothermy)

Within limits, most ecotherms can adjust metabolic rates to alter body temperature

Temperature compensation involves complex biochemical and cellular adjustments

Fish, salamanders maintain activity in warm or cold water