Human Physiology
Homeostatic regulation
Homeostasis → the process aims to maintain an internal environment within regulated
boundaries, and by that enable organisms to cope with external challenges.
Components of the regulation loop
1. Regulated variable
a. Any variable for which sensors are present
2. Stimulus
a. Any change in the regulated variable
3. Sensor
a. An element that is sensitive to changes in the regulated variable and
includes a signal proportional to the stimulus.
4. Control centre
a. Receives and integrates information from all sensors and compares them
with a set point
i. Setpoint → a reference value that defines the calibration of the
regulated variable
5. Effector
a. A physical component that initiates changes in the regulated variable’s
value
Types of regulation
Thermoregulation
- Homeostatic control of core internal body temperature
Feedback Loops
Negative
- Tend to counter and dampen changes; keeps the system at an equilibrium state
Positive
- Enhance or amplify changes, moves the system away from its equilibrium state,
and makes it more unstable
- Example: oxytocin release in childbirth
, Cardiovascular system
● Local:
○ similarities and differences between arteries and veins
■ Arteries
● Deliver oxygenated blood to organs
● Thick-walled structure with extensive development of elastic
tissue, smooth muscle, and connective tissue
● Receive blood directly from the heart and under the highest
pressure
● The volume of blood contained in the arteries is called
stressed volume
■ Veins
● Thin-walled structures
● Less elastic tissue → bigger capacity to hold blood
● Contain valves that maintain a unidirectional flow of blood
■ Similarities
● Both are covered in muscular tissues which assist in the
contraction or expansion go blood vessels
● Both undergo vasoconstriction or vasodilation depending on
the hormones and neurotransmitters released
● Transport of blood is unidirectional
○ relationships between flow (Q), resistance (R), and pressure (P)
■ Blood flow is determined by the pressure difference between the
two ends of the vessel and the resistance of the vessel to blood
flow.
, ● Q=P/R
■ Increasing resistance decreases blood flow
■ The longer the blood vessel, the greater the resistance
■ Viscosity increases resistance
○ how vessel’s properties affect blood pressure
■ Compliance
● The greater the compliance of an artery, the more effective it
is able to respond to changes in blood pressure
● Decrease in compliance, higher blood pressure
■ Length
● The smaller the vessel, the higher the pressure
■ Viscosity of blood
● Thicker blood (higher viscosity) increases blood pressure
○ structure and function of the heart (valves and their location and function,
cardiac cycle etc.)
■ Four chambers; two atria and two ventricles
● Right Atrium
○ Receives deoxygenated blood from the superior and
inferior vena cava, and from coronary veins.
● Left Atrium
○ Receives oxygenated blood from the four pulmonary
veins
● Right ventricle
○ Receives deoxygenated blood and pump it through
the pulmonary artery
● Left Ventricle
○ Receives oxygenated blood from the left atrium and
pumps it into the aorta
■ Four Valves: two atrioventricular valves and two semilunar valves
● Tricuspid [AV]
○ Located between the right atria and right ventricle
○ Open in atrial contraction and closes in ventricular
contraction
● Pulmonary
○ Located between the right ventricle and the
pulmonary orifice
○ Closes in atrial contraction and opens in ventricular
contraction
● Bicuspid (Mitral) [AV]
, ○ Located between the left atria and left ventricle
○ Open in atrial contraction and closes in ventricular
contraction
● Aortic
○ Located between the left ventricle and the ascending
aorta
○ Closes in atrial contraction and opens in ventricular
contraction
■ Cardiac Cycle
● Cardiac Diastole
○ The entire heart is relaxed
○ Blood enters at low-pressure through the veins
○ AV (tricuspid & bicuspid) valves are opened; blood
enters the ventricles
● Atrial Systole
○ Atria contracts and blood enters the ventricles
○ Pressure in the ventricles shut the atrioventricular
valves to prevent backflow
● Ventricular Systole
○ Ventricles contract from the bottom of the heart
○ Pressure in the ventricles increases that above the
arteries
○ Blood flows through the aortic and pulmonary valves
and leaves the heart
Homeostatic regulation
Homeostasis → the process aims to maintain an internal environment within regulated
boundaries, and by that enable organisms to cope with external challenges.
Components of the regulation loop
1. Regulated variable
a. Any variable for which sensors are present
2. Stimulus
a. Any change in the regulated variable
3. Sensor
a. An element that is sensitive to changes in the regulated variable and
includes a signal proportional to the stimulus.
4. Control centre
a. Receives and integrates information from all sensors and compares them
with a set point
i. Setpoint → a reference value that defines the calibration of the
regulated variable
5. Effector
a. A physical component that initiates changes in the regulated variable’s
value
Types of regulation
Thermoregulation
- Homeostatic control of core internal body temperature
Feedback Loops
Negative
- Tend to counter and dampen changes; keeps the system at an equilibrium state
Positive
- Enhance or amplify changes, moves the system away from its equilibrium state,
and makes it more unstable
- Example: oxytocin release in childbirth
, Cardiovascular system
● Local:
○ similarities and differences between arteries and veins
■ Arteries
● Deliver oxygenated blood to organs
● Thick-walled structure with extensive development of elastic
tissue, smooth muscle, and connective tissue
● Receive blood directly from the heart and under the highest
pressure
● The volume of blood contained in the arteries is called
stressed volume
■ Veins
● Thin-walled structures
● Less elastic tissue → bigger capacity to hold blood
● Contain valves that maintain a unidirectional flow of blood
■ Similarities
● Both are covered in muscular tissues which assist in the
contraction or expansion go blood vessels
● Both undergo vasoconstriction or vasodilation depending on
the hormones and neurotransmitters released
● Transport of blood is unidirectional
○ relationships between flow (Q), resistance (R), and pressure (P)
■ Blood flow is determined by the pressure difference between the
two ends of the vessel and the resistance of the vessel to blood
flow.
, ● Q=P/R
■ Increasing resistance decreases blood flow
■ The longer the blood vessel, the greater the resistance
■ Viscosity increases resistance
○ how vessel’s properties affect blood pressure
■ Compliance
● The greater the compliance of an artery, the more effective it
is able to respond to changes in blood pressure
● Decrease in compliance, higher blood pressure
■ Length
● The smaller the vessel, the higher the pressure
■ Viscosity of blood
● Thicker blood (higher viscosity) increases blood pressure
○ structure and function of the heart (valves and their location and function,
cardiac cycle etc.)
■ Four chambers; two atria and two ventricles
● Right Atrium
○ Receives deoxygenated blood from the superior and
inferior vena cava, and from coronary veins.
● Left Atrium
○ Receives oxygenated blood from the four pulmonary
veins
● Right ventricle
○ Receives deoxygenated blood and pump it through
the pulmonary artery
● Left Ventricle
○ Receives oxygenated blood from the left atrium and
pumps it into the aorta
■ Four Valves: two atrioventricular valves and two semilunar valves
● Tricuspid [AV]
○ Located between the right atria and right ventricle
○ Open in atrial contraction and closes in ventricular
contraction
● Pulmonary
○ Located between the right ventricle and the
pulmonary orifice
○ Closes in atrial contraction and opens in ventricular
contraction
● Bicuspid (Mitral) [AV]
, ○ Located between the left atria and left ventricle
○ Open in atrial contraction and closes in ventricular
contraction
● Aortic
○ Located between the left ventricle and the ascending
aorta
○ Closes in atrial contraction and opens in ventricular
contraction
■ Cardiac Cycle
● Cardiac Diastole
○ The entire heart is relaxed
○ Blood enters at low-pressure through the veins
○ AV (tricuspid & bicuspid) valves are opened; blood
enters the ventricles
● Atrial Systole
○ Atria contracts and blood enters the ventricles
○ Pressure in the ventricles shut the atrioventricular
valves to prevent backflow
● Ventricular Systole
○ Ventricles contract from the bottom of the heart
○ Pressure in the ventricles increases that above the
arteries
○ Blood flows through the aortic and pulmonary valves
and leaves the heart
