The Endocrine System Pt. 1

Hormones

chemical messengers that travel through the blood to affect distant target cells

Control enzyme activity

When hormones change the activity of proteins already in a cell they,

Control membrane transport

when hormones change the movement of ions or molecules across cell membranes, they

Control gene expression and protein synthesis

when hormones, change which proteins a cell produces, they

Target cell

A cell with the appropriate receptor for a hormone

Receptor

A protein that binds a specific hormone or signal

Hormone degradation

Breakdown of a hormone into inactive metabolites

Endocrine reflex

A pathway that connects a stimulus to hormone secretion and a physiological response

Peptide and protein hormones

• Made from amino acids.

• Most hormones belong to this class, according to your slides.

• Generally bind to receptors on the cell membrane.

• Often use second messengers such as cAMP.

• Can activate signal transduction pathways that change enzyme activity and cell function.

Examples: Insulin, growth hormone, and antidiuretic hormone.

Steroid hormones

• Derived from cholesterol.

• Lipophilic, meaning they can pass through cell membranes.

• Usually bind to receptors in the cytoplasm or nucleus.

• Hormone-receptor complexes can regulate gene expression.

• Usually have slower-onset, longer-lasting effects.

• Often travel in blood bound to protein carriers.

Examples: Cortisol, estrogen, and testosterone.

Amine hormones

• Derived from the amino acids tyrosine or tryptophan.

• Relatively small molecules.

• Include catecholamines and thyroid hormones.

Examples: Epinephrine, norepinephrine, melatonin, and thyroid hormones T3 and T4.

Step 1 of Peptide Hormone Synthesis

Preprohormone formation: Ribosomes use mRNA to assemble an amino acid chain called a preprohormone

Step 2 of Peptide Hormone Synthesis

Entry into the ER: A signal sequence directs the preprohormone into the endoplasmic reticulum

Step 3 of Peptide Hormone Synthesis

Prohormone Formation: The signal sequence is removed, producing an inactive pro hormone

Step 4 of Peptide Hormone Synthesis

Golgi Processing: The pro hormone passes through the Golgi complex and is packaged into secretory vesicles

Step 5 of Peptide Hormone Synthesis

Activation: Enzymes process the pro hormone into one or more active peptide hormones

Step 6 of Peptide Hormone Synthesis

Release: Secretory vesicles release the hormone by exocytosis. The hormone enters the blood and travels to target tissues

Cell-surface receptors

• Hormone binds its receptor.

• The receptor activates intracellular signaling proteins.

• Second messengers or protein kinases relay the signal.

• Existing proteins change activity, and sometimes gene expression changes.

• The target cell produces a physiological response.

• Water-soluble hormones, including many peptide hormones, generally cannot pass directly through the lipid cell membrane. Instead, they bind to

Intracellular Receptors

• The hormone enters the target cell.

• It binds to a cytoplasmic or nuclear receptor.

• The hormone-receptor complex regulates gene expression.

• New mRNA is produced.

• Translation produces proteins that change cell function.

• Steroid hormones generally cross the cell membrane and bind to

Step 1 of Endocrine Reflex

Stimulus: A change occurs in the body's internal environment.

Step 2 of Endocrine Reflex

Afferent signal: Information reaches the control center.

Step 3 of Endocrine Reflex

Integration: The control center processes the information.

Step 4 of Endocrine Reflex

Efferent signal: A hormone is released.

Step 5 of Endocrine Reflex

Physiological action: Target tissues respond.

Step 6 of Endocrine Reflex

Negative feedback: The response reduces the original stimulus.

The Pineal Gland

A small gland near the roof of the third ventricle in the brain.

Hypothalamus

links the nervous system to the endocrine system. It regulates pituitary activity and helps coordinate hormone secretion.

Hypothalamic stimulation

Signals from the central nervous system influence the hypothalamus.

Pituitary stimulation

Hypothalamic hormones regulate the pituitary

Endocrine gland stimulation

Pituitary tropic hormones stimulate other endocrine glands.

Anterior Pituitary

Synthesizes and secretes its own hormones in response to hypothalamic regulation, Includes growth hormone, also secretes hormones that regulate other endocrine glands.

Posterior Pituitary

Stores and releases hormones made by hypothalamic neurons, Releases antidiuretic hormone ADH/Vasopressin, also releases oxytocin.

IGF-1 (insulin-like growth factor 1)

is produced by the liver and other tissues. It contributes to GH's growth-promoting effects.

Step 1 of GH and IGF-1 Signaling

Growth hormone released from anterior pituitary

Step 2 of GH and IGF-1 Signaling

GH binds its receptor on target cells

Step 3 of GH and IGF-1 Signaling

JAK-STAT signaling promotes gene expression

Step 4 of GH and IGF-1 Signaling

Increased IGF-1 production and tissue growth

Long-Bone Growth

• Chondrocytes divide and produce cartilage.

• Older cartilage becomes calcified and is replaced by bone.

• Osteoblasts deposit new bone tissue.

  • The bone increases in length while the growth plate remains open.

Epiphyseal Plates

linear growth of long bones takes place at the

Dwarfism due to GH Deficiency

Too little GH during childbirth, causes reduced linear growth

Gigantism

Excess GH during childhood, before growth plates close, causes excessive height and long-bone growth

Acromegaly

Excess GH in adults, after growth plates close, causes enlargement of hands, feet, and facial bones and tissues.

Colloid

The thyroid gland contains follicles lined with follicular cells and filled with a substance called

Follicular Cells

Hormone T3 and T4, regulate metabolism, growth, and development

Parafollicular (C) Cells

Calcitonin, Participates in calcium regulations

Deiodinases

T4 can be converted into the more active T3 by enzymes called … which remove an iodine atom.