HUBS191 Lecture 25: Endocrine System 1 - Introduction

Flashcards covering key concepts from the Endocrine System 1 lecture, including homeostasis, ECF variables, hormone classes, and hormone action mechanisms.

Homeostasis

The maintenance of relatively constant conditions in the internal environment (ECF) in the face of external (or internal) change.

Why is blood glucose important?

ATP production, particularly for brain function.

What is the normal range for blood glucose?

3.5 – 6 mmol/L (fasting), 3.5 – 8 mmol/L (non-fasting)

Why is Sodium (Na+) important?

ECF volume, action potential generation.

What is the normal range for Sodium (Na+)?

135 – 145 mmol/L

Why is Calcium (Ca++) important?

Structural component of bone and teeth, neurotransmission and muscle contraction, blood clotting and enzyme function.

What is the normal range for Calcium (Ca++)?

2.2 to 2.6 mmol/L

Why is Potassium (K+) important?

Main determinant of RMP, nerve and muscle function.

What is the normal range for Potassium (K+)?

3.5 to 5 mmol/L

Why is ECF osmolarity important?

Maintenance of normal cell volume.

What is the normal range for ECF osmolarity?

275-300 mosmol/L

What is a 'Regulated variable'?

The variable the system senses and tries to keep stable.

What is a 'Set point'?

The target value for a regulated variable.

What is a 'Reference range'?

Values of the regulated variable within ‘normal’ limits.

Inter-individual variation

Variation in set points between individuals.

Intra-individual variation

Fluctuations around the set point in response to normal activity within an individual.

Circadian Rhythm

Cycles of 24 hours.

What is considered a 'normal' reference range?

Values within two standard deviations of the mean.

Function of Sensors in homeostatic control

Monitor the regulated variable and detects deviation from set-point.

Function of Control centre/integrator in homeostatic control

Compares the variable’s actual value to the set-point and sends signals to effectors if correction is required.

Function of Effectors in homeostatic control

Act to oppose the effect of the stimulus, thereby correcting the change and restoring the variable to its set-point.

Negative Feedback

Opposes change and move regulated variable back toward its set point.

Positive Feedback

Reinforces the initial change, moving the variable further away from the set point.

Feed forward Homeostatic Control

Detection or anticipation of conditions that could disrupt homeostasis, taking preemptive action.

Nervous system

Neurons produce APs and release neurotransmitter at synapses, resulting in fast signaling.

Endocrine system

Hormones are released into the blood and bind to receptors on target cells, resulting in slower, longer-lasting action.

Local Hormones

Act locally on other nearby cells (paracrines) or on the same cell that secreted them (autocrines).

Amino acids that can be modified to synthesize hormones

Tyrosine, Tryptophan and Histadine

Peptide hormones

Chains of 3 to 49 amino acids.

Protein hormones

Chains of 50 to 200 amino acids.

How are protein and peptide hormones synthesized?

Synthesized on ribosomes of RER as larger preprohormones, cleaved to prohormones in ER, then packaged into secretory vesicles in Golgi apparatus where they are cleaved into active hormone and inactive fragments.

Steroid hormones

Derived from cholesterol and are lipid soluble.

What does the response to a hormone depend on?

What receptors are present and their ‘intracellular machinery’

Mechanism of action for lipid soluble hormones

Diffuse through the lipid bilayer, bind to receptors in the cytoplasm or nucleus, alter gene expression, and produce new proteins.

Mechanism of action for water soluble hormones

Bind to membrane receptors, activating a G protein and causing the production of a second messenger inside the cell such as cyclic AMP (cAMP) or calcium ions (Ca++).

G-protein coupled receptors

Transmembrane proteins coupled to G-proteins that activate enzymes (e.g., adenylate cyclase) or alter ion channel activity to produce second messengers.