Homeostasis

Homeostasis

Maintenance of relatively stable internal environment

Active Homeostasis

Relatively constant conditions that involve specific sensing/controlling mechanisms

Passive Homeostasis

Relatively constant conditions that lack specific sensing/controlling mechanisms

Negative Feedback Control

Work to restore homeostasis upon the deviation of regulated parameter

True

T/F: (-) feedback mechanisms are the major control process used to maintain homeostasis

Heart rate, arterial (blood) pressure

Arterial baroreflex parasympathetic effects include a decrease in __ __ and __ __

Heart rate, vasoconstriction

Arterial baroreflex sympathetic effects include an increase in __ __ and associated __

Pressure

baroreceptors

afferent

medulla

90

efferent

heart, vessels

cardiac, peripheral

Arterial baroreceptor negative feedback loop

• Regulated variable = Blood __

• Sensor = __ in carotid arteries and aortic arch

• Input signal = Sensory __ nerves

• Control center = cardiovascular center in __

• Error detector = set point around __ mm Hg that resets over time

• Output signal = Parasympathetic and sympathetic __ nerves, epinephrine

• Effectors = __ and blood __

• Controlled variables = __ output and total __ resistance

Heart rate

__ __ is not homeostatically regulated as there is no internal sensor

Glucose, 2, pancreatic, beta, cells, 70-140, insulin, muscle, up, up, down, down

Fed-state glucose negative feedback loop

• Regulated variable = __ level

• Sensor = GLUT-_ Receptors, __ beta cells

• Input signal = Pancreatic __ cells

• Control center = Pancreatic beta __

• Error detector = set point around __-__ mg/dL

• Output signal = __

• Effectors = __/adipose, liver, other tissues

• Controlled variables = _ GLUT-4 receptors, _ glycogenesis, _ glycogenolysis, _ gluconeogenesis (up vs down)

Detection, glycogen

In the fed-state glucose loop, we aim to increase glucose __ and need of __ breaking down glucose

Glucose, pancreatic, alpha, cells, 70-99, glucagon, muscle, up, up

Fasted-state glucose negative feedback loop

• Regulated variable = __ level

• Sensor = __ alpha cells

• Input signal = Pancreatic __ cells

• Control center = Pancreatic alpha __

• Error detector = set point around __-__ mg/dL

• Output signal = __

• Effectors = liver/__, other tissues

• Controlled variables = _ glycogenolysis, _ gluconeogenesis (up vs down)

Glucose, glycogen

In the fasted-state glucose loop, we aim to increase concentrations of __ and halt production of __

Body temperature

Example where disturbances exceed the capacity of negative feedback loops to maintain homeostasis —> Unable to cool sufficiently so unregulated

Nested homeostasis

Many physiological variables are involved in multiple, overlapping feedback loops

Regulated, controlled

PCO2 is a __ variable in the PCO2 homeostatic system

PCO2 is a __ variable in the pH homeostatic system

pH, PCO2, PCO2

__ (PCO2 or pH) is more important than __ (PCO2 or pH) for cellular viability, and can thus override the __ homeostatic system

Positive Feedback Loops

Hormone’s effects lead to additional release of hormone onward

Childbirth

Cervical stretch → oxytocin → stimulates contraction → oxytocin → parturition

(+ feedback)

Ovulation

Estrogen → FSH/LH → Estrogen → Until this event…

(+ feedback)

Non-hormonal

Na+ channel opening → depolarization → Action potential → next Na+ channel open

(+ feedback)

Mean arterial pressure (Pa)

Driving force for blood flow

CO x TPR

Arterial pressure (Pa) formula

Cardiac output

Variable of Pa measured by heart rate and contractility

Total peripheral resistance

Variable of Pa measured by vessel diameter

Carotid, aortic

Baroreceptors are pressure sensors located within the walls of the __ sinus and __ arch

Medulla

Component of baroreceptor reflex that compares actual pressure to “set point” and initiates an appropriate response with either SNS or PNS