Download Chapter 45 Hormones and the Endocrine System

Chapter 45
Hormones and the
Endocrine System
Intercellular communication
• The endocrine system releases hormones into the
blood. Regulate growth, development & organism
processes
– Hormones can reach all cells
– Response is slow
– Action can remain a long time
• The nervous system releases neurotransmitters that
affect specific neuronal cells.
– Neurotransmitters reach few cells
– The response is rapid
– The action is brief
Nervous system overlap
• Neurosecretory cells found in the brain also
release hormones called neurohormones
• Some neurohormones also f(x) as
neurotransmitters.
• Nervous system plays a role in regulating
some parts of the endocrine system
– Regulation of circadian and seasonal rhythms
– Regulation of reproductive cycles
Intercellular signaling
• Endocrine Signaling: Secreted into
blood, act anywhere
• Paracrine Signaling: Diffuse locally
& trigger response in neighboring
cells
• Autocrine Signaling: Diffuse locally
& trigger response in secreting cell
• Synaptic Signaling:
Neurotransmitters, diffuse across
synapse
• Neuroendocrine Signaling:
Neurohormones diffuse into blood,
act anywhere (secreted from nerve
cells.
Types of secreted signaling
hormones
• 3 classes of hormones
– Proteins and peptides (under 30 aa’s)
– Amines (derived from a single aa)
– Steroids
• Pheromones are volatile signals between organisms
Types & Chemical classes of hormones
• Water soluble hormones
bind to plasma membrane
receptors
– Proteins & peptides under 30 aa
– Amines, derived from a single aa
• Steroid hormones bind to
intracellular receptors, lipid
soluble
– Derived from cholesterol
– Act inside a cell membrane
• Pheromones are signals
between organisms
Water soluble
hormones Fig. 45.5a
• Intracellular response can be
– Activation of an enzyme
– Change in uptake or secretion
of chemicals
– Rearrangement of cytoskeleton
– Transcription of particular
genes
Water soluble hormones
• Can activate second messenger pathways
Lipid soluble
hormones
Fig. 45.5b
• Diffusion
• Formation of
hormone/receptor complex
• Activation of transcription
• Production of mRNA
Different effects from one hormone
Human endocrine glands
Simple hormonal pathway
Glucose homeostasis
• Glucagon and insulin are produced in 2% of the
cells in the pancreas
– Islets of Langerhans are scattered throughout the
pancreas
– Glucagon is produced by alpha cells
– Insulin is produced by beta cells
• Glucagon and insulin are antagonistic hormones
that regulate glucose in the blood at
90mg/100mL
Effects of insulin and glucagon
• Insulin stimulates all body cells except brain cells
to take up glucose
• Insulin slows glycogen breakdown in the liver
• Insulin inhibits gluconeogenesis and production
of glucose from glycerol.
• Glucagon increases glucose in the blood.
– Glucagon stimulates hydrolysis of glycogen in the
liver and conversion of amino acids and glycerol to
glucose
– Only liver cells are sensitive to glucagon.
Glucose
homeostasis
Diabetes
• Diabetes mellitus has two different causes
1. Type I the immune system destroys beta cells
leading to lack of insulin
2. Type II is a deficiency of insulin or reduced
sensitivity of insulin receptors
• Glucose levels in the blood exceed the
reabsorbing abilities of the kidney
• The body turns to fat to produce glucose,
which produces acidic blood (ketosis)
Endocrine and nervous system
interactions in vertebrates
Hypothalamus and posterior pituitary
• The hypothalamus is
the relay between the
nervous & endocrine
systems
• Axons project to
posterior pituitary and
release neurohormones
– Antidiuretic hormone
(ADH)
• Promotes water retention
in kidneys
– Oxytocin
• Uterine contractions &
milk production
Hypothalamus and anterior pituitary
Tropic: affects
endocrine glands
Anterior pituitary: Tropic hormones
• Gonadotropins--Follicle stimulating hormone
(FSH) and leutinizing hormone (LH) stimulate
activities of ovaries and testes
• Thyroid stimulating hormone (TSH) stimulates
production and relase of thyroid hormones
• Adrenocorticotropic hormone (ACTH)
promotes production and secretion of steroid
hormones from the adrenal gland.
Anterior pituitary
• Growth Hormone: (tropic & nontropic):
– Stimulate bone & cartilage growth in children
– Regulates metabolism in adults
• Hypothyroid: lethargic
• Hyperthyroid: Graves Disease
• Non-Tropic Hormones:
– Prolactin stimulates mammary gland growth and
milk synthesis in mammals.
– Melanocyte stimulating hormone inhibits hunger
 b-endorphins dull the perception of pain (some
drugs cause the brain to secrete)
Thyroid hormone T3 & T4
• Plays an important role in development
– Controls metamorphosis of tadpole into frog.
• Required in bone formation and
branching of neurons during
development
– Inherited conditions of thyroid deficiency can
lead to cretinism
• Maintains homeostasis in blood pressure,
heart rate, muscle tone, digestion and
reproduction
• TH increases oxygen use and cellular
metabolism.
• Graves’ disease is hyperthyroidism.
• Hypothyroidism leads to weight gain,
lethargy
Calcium Regulation
• Thyroid Hormone: Calcitonin
– Increases activity of osteoblasts
that increase bone deposition.
• Parathyroid hormone (PTH)
leads to release of calcium
into the blood.
– Breaks down bone & slows
bone growth
– Stimulates liver and kidney to
produce calcitriol from Vitamin
D
• Calcitriol increases absorption of
calcium in the GI tract.
Adrenal gland and short term stress
Adrenal gland and long term stress