Overview
This lecture covers the structure and function of nervous tissue, the organization of peripheral nerves, and the anatomy and hormone secretion of major endocrine glands.
Nervous Tissue Types and Cells
- Nervous tissue is found in the brain, spinal cord, and peripheral nerves.
- Two main cell types: neurons (functional, transmit electrical impulses) and glial cells (supportive).
- Neurons contain chromatophilic substance (stained rough ER and ribosomes).
- Glial cells protect, nourish, and support neurons.
Glial Cells in CNS and PNS
- Astrocytes (CNS): attached to blood vessels, provide structural/nutritional support, and help form the blood-brain barrier.
- Neurolemocytes (Schwann cells, PNS): create myelin sheath, increase conduction via saltatory conduction at nodes of Ranvier.
- Satellite cells (PNS): surround neuron cell bodies in the dorsal root ganglion, provide support similar to CNS astrocytes.
Structure of Peripheral Nerves
- Endoneurium: covers individual axons.
- Perineurium: surrounds a fascicle (bundle of axons).
- Epineurium: encloses the entire nerve (bundles of fascicles).
Endocrine Glands Overview
- Thymus: secretes thymosins for lymphocyte development (large in children, shrinks with age).
- Pituitary gland: anterior lobe (acidophils secrete GH/prolactin; basophils secrete TSH, ACTH, FSH, LH), posterior lobe releases ADH and oxytocin.
- Pineal gland: contains pinealocytes; secretes melatonin for circadian rhythm regulation.
- Thyroid: follicular cells secrete T3/T4 (regulate metabolism); parafollicular cells secrete calcitonin (lowers blood calcium).
- Parathyroid: chief cells secrete PTH (increase blood calcium, decrease phosphate by stimulating osteoclasts and calcitriol synthesis).
Adrenal Gland Structure and Hormones
- Adrenal medulla: secretes epinephrine/norepinephrine (fight or flight).
- Adrenal cortex:
- Zona glomerulosa: secretes aldosterone (increases Na+, decreases K+).
- Zona fasciculata: secretes cortisol (maintains glucose, anti-inflammatory).
- Zona reticularis: secretes androgens (reproductive organ development).
Pancreatic Endocrine Function
- Pancreatic islets contain:
- Alpha cells: secrete glucagon (raise blood glucose).
- Beta cells: secrete insulin (lower blood glucose).
- Delta cells: secrete somatostatin (regulates alpha/beta cells by inhibiting hormone release).
Key Terms & Definitions
- Neuron — functional nerve cell that transmits electrical impulses.
- Glial cells — supportive nerve cells in CNS and PNS.
- Astrocyte — CNS glial cell, supports blood-brain barrier.
- Neurolemocyte (Schwann cell) — PNS glial cell, produces myelin sheath.
- Endoneurium/Perineurium/Epineurium — connective tissue coverings of nerves.
- Follicular cells — thyroid cells secreting T3/T4.
- Parafollicular cells — thyroid cells secreting calcitonin.
- Chief cells — parathyroid cells secreting PTH.
- Pinealocyte — pineal gland cell, secretes melatonin.
Action Items / Next Steps
- Identify all discussed structures on histology slides.
- Memorize hormones and their functions for each endocrine gland.
- Prepare for the upcoming quiz on structures, hormones, and their functions.