Need to Know

Homeostasis

maintaining a relatively constant internal environment in the presence of changing external conditions

Homeostasis is maintained by

negative feedback loops

Even in the presence of a changing environment

the inside of the body stays relatively constant or within a tight range by changing.

Homeostasis does not involve

keeping conditions static but rather within a tightly regulated range

Most diseases involve the

disruption of normal homeostasis

When a disease or virus, such as the flu

causes the body to lose its ability to maintain homeostasis, leading to symptoms such as fever and fatigue.

When you are thrown off

a 4is set in motion to get you back to equilibrium

Set Point

The optimal condition or range in which a physiological system operates, maintaining stability and homeostasis.

Sensor

• something that detects stimulus

• signals the control center

Control Center

• processing center (nervous system)

• triggers a response

Effector

• a cell (muscle or gland) that performs the body’s response

IF you go outside in the summer, it might be above your body temperature

This may cause you to start sweating if you stay outside for awhile. Evaporating cools your body.

If this did not happen, its dangerous and even deadly, and you might end up in the hospital

Feedback Loop

Negative Feedback Loop

A change in a variable triggers a response that counteracts that change and maintains homeostasis

When the response opposes (or reduces) the stimulus

Positive Feedback Loop

A change in a variable triggers a response that amplifies that change

When the response enhances the stimulus

Example of Negative Feedback Loop

Homeostasis

Example of Positive Feedback Loop

Childbirth and Blood Clotting

Thermoregulation

how animals maintain an internal temperature within an acceptable range

REGULATORS

generate their own heat internally (river otter)

CONFORMERS

warmed by heat from an external source or other ways (bass)

Humans are

regulators that maintain a stable internal body temperature

Endotherms

generate heat INTERNALLY

 Regulation of body temperature through metabolism, body

response system (and behaviorally)

 Mammals and birds

Ectotherms

gain most of their heat from the external environment

 Regulation of body temperature MOSTLY through behavior

 Amphibians, fish, reptiles, invertebrates

Ectotherms DO

regulate body temperature by behavior but NOT internally through metabolism

Example in butterflies

warming up flight muscles

This does not happen in birds and mammals! Why? They are endotherms.

Cost of thermoregulating

More energy is expended due to need for more metabolism to keep body regulated

Four processes regulate body temperature in ectotherms

conduction, convection, radiation, and evaporation

 Radiation

heat transfer from a warmer object to a cooler one

 Example: Absorbing heat from the sun --> warming

Evaporation

vaporization of water from a surface (heat is released)

 Example: Sweat evaporating from skin --> cooling

Conduction

heat transfer between two objects by direct contact

 Example: Sitting on a warm rock --> warming

 Example: Sitting on cool concrete --> cooling

 Convection

heat transfer through movement of air or liquid (not direct contact)

 Example: Feeling a cool breeze (fan) on a hot day --> cooling (pushes heat away from body)

 Example: Blood moves heat from the body core to extremities

endotherm and ectotherm are not

mutually exclusive

•Insulation in endotherms

reduces the flow of heat between the body and environment. Hair & layers of adipose (fat) in mammals

Feathers in birds

Vasodilation

widening of blood vessels near surface of body; enhances heat loss

Vasoconstriction

decrease in diameter of blood vessels reduces blood flow and heat loss

Types of Thermoregulation

Insulation, Evaporation, Behavioral, and Circulatory

Nerve cells in the hypothalamus

serve as a thermostat

How can a fever be maintained for hours to days?

Your body changes its set point if you have an infection.

It reprograms its thermostat to stay at a higher temperature to possibly slow down pathogens. Scientists are not sure why

What happens when your fever breaks?

You sweat to cool down. (negative feedback!)

Two major systems coordinate and control responses to stimuli and maintain homeostasis (Mind/Brain-Body connection!)

The endocrine and nervous systems

Endocrine system

 Signaling molecules travel directly via blood affecting

various cells with receptors

 Acts “globally”

 Slower, but long-lasting

Nervous system

 Electrochemical signaling travels to a specific location

affecting neurons or muscle/gland cells

 Acts “specifically”, along dedicated routes

 Faster, but fleeting

Endocrine and Nervous System can

work together

SIGNALING MOLECULES

Endocrine System - Hormones

Nervous System - Neurotransmitters and Neurohormones

Hormones

 Released by cells of the endocrine system

 Travel in the bloodstream and affect target cells

Neurotransmitters

 Act on other neurons, muscles or glands.

 Travel very short distance across a synapse

Neurohormones

 Released by neurosecretory cells

 Travel in the bloodstream

TWO TYPES: HORMONE SIGNALING MOLECULES

Peptide and Steroid

Peptide hormones (amino acid based)

 Water soluble

• Cannot travel through plasma membrane

 Bind to the receptor in the membrane of the target cell

 Triggers signal transduction (second messenger, kinases, etc)

Steroid hormones (lipids)

 Lipid soluble

 Travel through the plasma membrane into the target cell

 Bind to the receptors in the cytoplasm or inside the nucleus

 Acts as transcription factor

signal transduction

It is a chain reaction from one protein to another to convert an extracellular signal to an intracellular one….turn on a gene inside the cell

Which kind of molecules will go more easily through the cell membrane?

Small and Hydrophobic Molecules

Is the blood hydrophilic or hydrophobic?

75% water-hydrophilic

Which type of hormone travel easier into the bloodstream?

Peptide hormones flow directly in bloodstream.

Steroid binds to a carrier protein that

escorts them through the blood

A single hormone can create different responses in different cells, based on

1. The receptor it interacts with

2. The relay proteins involved in the

signaling pathway.

 Ex: Epinephrine (Adrenaline)

 Elicits the Fight-or-Flight Response

Fight or flight is not good for diabetics. Think about that and let me know why?

Likely not a good thing. Epinephrine increase blood glucose

Are you hungry when you are stressed or running from a predator?

No

Simple endocrine pathway

•A stimuli causes endocrine cells and

glands to release a peptide hormone

(secretin).

•Digestion: Partially processed food

(highly acidic juices) triggers this

Steps of Secretin Signaling

1. Low pH on duodenum

2. Secretin is release from your

duodenum (of small intestine)

3. Secretin target pancreatic cells to

release bicarbonate to neutralize

the pH in the intestines.

4. This is negative feedback to keep

your small intestine the right pH!

alpha cells secrete

glucagon in response to low blood sugar levels.

beta cells secrete

insulin in response to high blood sugar levels.

Insulin

is a peptide hormone secreted by the beta cells of the pancreas. It is in a control system that helps keep blood glucose from rising too high

GLUCOSE REGULATION

• Controlled by 2

different hormones (Alpha and Beta Cells)

• Both produced in the

pancreas

You can breakdown fat to

live without food for weeks

Diabetes mellitus

blood glucose levels too high

Type I Diabetes

 Loss of insulin-producing cells (autoiummune disease or viral

infection)

 Insulin shots required & diet must be monitored

Type II Diabetes

 Cells resist the influence of insulin & do not take up glucose

 Pancreas overproduces insulin and becomes desensitized

 Diet change, weight loss, exercise can reverse (but may be

genetic)

 7th most common cause of death in the US

Exchange processes between organisms and their environment often occur

passively (or actively) through the physical process of diffusion. This does not require an energy input

Substances move from high concentration to lower concentration by

passive diffusion until they reach equilibrium. (e.g., oxygen diffusing into a cell)

SLOW PROCESS. How do we maximize diffusion overall?

• shorten the diffusion distance

• have a steeper concentration gradient

• increase in surface area

Basal Metabolic Rate

the amount of energy an animal uses in a unit of time (base level to stay alive). This is the rate when you are not exercising or stressed out

An ectotherm requires

much less energy per kilogram than does an endotherm of equivalent size

A small endotherm has a much greater energy demand per kilogram than does a

large animal of the same class (e.g., hummingbird vs hawk). due to a higher surface : volume ratio (hummingbird loses heat faster)

Ectotherms have a much lower metabolic rate than

endotherms of comparable size

Chemoheterotrophs

Organisms that depend on organic chemicals to generate energy/ATP

Food processing involves

Ingestion, Digestion, Absorption (Transport), and Elimination

Ingestion

the act of eating or feeding

Digestion

when food is broken down into small molecules (mechanical and chemical)

Absorption (Transport)

when cells take up small molecules (and deliver to body cells)

Elimination

passing of undigested material out of the digestive system

If a person is on life support receiving food intravenously, which of the 4 steps are skipped?

Ingestion, Digestion, and Absorption

Two Types of Digestion

Mechanical and Chemical

Four basic ways to ingest

• Substrate feeding-live in or

on their food source

• Suspension feeding-filter,

capture or trap food

• Fluid feeding-suck fluid

nutrients from a host

• Bulk feeding-consume large

pieces of food (most)

Humans are what type of feeders

Bulk feeders, consuming large pieces of food.

Chemical digestion is known as

Hydrolysis

Mechanical digestion

breaks food into smaller pieces, increasing surface area exposes surfaces to chemical digestion

Chemical digestion

cleaves large molecules into smaller molecules (protein-→amino acids) using enzymes (enzymatic hydrolysis)

How Do We Safely Eat?

• Compartmentalization: Processing food within

intracellular or extracellular compartments.

• Food vacuoles are an example of intracellular

digestion. Food vacuoles plus digestive enzymes

break the food down safely. (Ex. Sponges)

• Most animals have extracellular digestion using a

long alimentary canal with compartments.

• Or BOTH (Ex. Hydra)

Simple body plans have a

gastrovascular cavity with a single opening

• Single opening EITHER takes in food OR expels waste

• Ex: Hydra uses tentacles, 2 specialized cells, enzymes, and food vacuoles

Complex body plans have an

alimentary canal with two separate openings

• One opening takes in food (mouth) and the other expels waste (anus)

• They can eat and digest at the same time.

• Ex: Earthworms, grasshoppers, birds, us

Most animals use an

alimentary canal with compartments that are continuous with the outside of the animals’ body

Digestion Begins in the

Oral Cavity

Teeth & tongue

• Chewing increases surface area for

enzymatic hydrolysis

• Tongue facilitates swallowing by forming and

pushing back the bolus

• Mechanical Digestion

Carnivores have

large, pointed incisors and canines to kill, rip, cut, etc

• Jagged premolars and molars crush and shred meat to digest it

Herbivores have

broad, ridged premolars to grind up plants

• Incisors and canines (if present) to bite

plants

Omnivores (US!) have

incisors for biting, canines for tearing, premolars for grinding, and molars for crushing

Salivary glands do

Chemical Digestion

Mucus (component of saliva)

lubricates food for swallowing & protects gums from abrasion