Session 7

Question 0

Discuss examples of biological rhythms

Answer 0

Blood cortisol - diurnal rhythm (peak in morning)
Biological clock (suprachiasmatic nucleus in hypothalamus)
Melatonin - light/dark cycle, hormone released from pineal gland
Menstrual cycle

Question 1

Describe the main features of control systems in the body

Answer 1

Communication - action potential, hormones
Control centre (hypothalamus in brain) - determines set point, analyses input, determines response
Receptor - stimuli –> sensor –> afferent pathway –> control centre
Effector - control centre –> efferent pathway –> effector
Feedback loops

Question 2

Define the term ‘hormone’ and list the features of communication processes involving hormones

Answer 2

Hormone - chemical messengers involved in communication that travel via the bloodstream
Rate of secretion controlled by negative feedback, have target cells

Question 3

List the classes of chemical substances which can act upon target cells

Answer 3

Polypeptide - single chain peptides e.g. growth hormone, insulin, TRH
Glycoprotein - two polypeptide chains with CHO side chains, released from anterior pituitary e.g. TSH, LH, FSH, hCG
Amino acid derivatives e.g. thyroid hormone, adrenaline, histamine
Steroid - derived from cholesterol but vary slightly e.g. calciferol, corticosteroids, progesterone, testosterone, oestrogen

Question 4

Explain, in general terms, the ways in which hormone secretion may be controlled

Answer 4

Negative feedback - rate of secretion

Question 5

Describe how hormones are transported and act upon target cells

Answer 5

Transported in the blood in very low concentrations
Peptide and amide hormones - water soluble
Steroid and thyroid hormones - insoluble
Bind to specific proteins (steroid - SBGs, thyroid - TBG) - increase solubility of hormone, half life and readily accessible reserve
Free form is biologically active
Hormones bind to receptors on or in target cells:
Cytoplasm receptor/nucleus receptor –> DNA –> mRNA –> response
Surface receptor –> 2nd messenger –> response
Response depends on concentration of active hormone, receptor number, affinity, degree of signal amplification

Question 6

Describe, in outline, the control of appetite

Answer 6

Appetite centre (satiety centre) in brain - arcuate nucleus in hypothalamus contains two neurones:
Primary - sense glucose, fatty acids in blood, respond to hormones
Secondary - synthesise input, coordinate response (down vagus nerve)

Question 7

Discuss the hormones involved in the control of appetite

Answer 7

Primary neurones:
Excitatory - neuropeptide Y (NPY), agouti-related peptide (AgRP) –> stimulate appetite
Inhibitory - pro-opiomelanocortion (POMC) –> B-endorphin (reward system) a-melanocyte stimulating hormone (aMSH) –> suppress appetite
Ghrelin - peptide hormone released from empty wall of stomach, stimulates excitatory
PYY - peptide hormone released from small intestine, suppresses appetite
Leptin - peptide hormone released from adipocytes, stimulates inhibitory (induces uncoupling proteins in mitochondria)
Insulin - suppresses
Amylin - peptide hormone secreted from B cells in pancreas, suppresses

Question 8

Discuss metabolic syndrome and it’s consequences

Answer 8

Pattern of symptoms in obese adults:
Insulin resistance (diabetes)
Dyslipidaemia (increased cholesterol and LDL)
Impaired glucose tolerance
Hypertension (>140/90)
Increased waist/hip ratio (central adiposity)

Question 9

Explain the Developmental Origins of Health and Disease Theory and Epigenetics

Answer 9

DOHaD: strong association between incidence of adult disease and birth weight and placenta weight, foetus adapts to conditions in utero (e.g. supply of nutrients) - low birth weight = CHD, hypertension, type 2 diabetes
Epigenetics: inherited phenotype resulting from changes in a chromosome without changes in the DNA sequence (e.g. DNA methylation, changes in histones structure –> suppression of gene transcription)