Overview
This lecture covers the structure and function of the endocrine system and the sensory systems of the brain, focusing on hormonal regulation, sensory perception, and related anatomical features.
The Endocrine System: Overview and Signaling
- Endocrine system uses chemical signaling with hormones, often slower but longer-lasting than neural signaling.
- Endocrine glands are ductless and secrete hormones into interstitial fluid, which then enter the bloodstream.
- Major endocrine glands include pituitary, thyroid, parathyroid, adrenal, pineal, pancreas, ovaries, and testes.
- Neural signaling is rapid and localized, while endocrine signaling can have widespread and varied effects.
Hormones: Types, Actions, and Regulation
- Three major classes of hormones: amines, peptides/proteins, and steroids.
- Amine and peptide/protein hormones are water-soluble; steroid and thyroid hormones are lipid-soluble.
- Lipid-soluble hormones use intracellular receptors; water-soluble hormones use cell membrane receptors and second-messenger pathways (e.g., cAMP, IP3).
- Hormone secretion is regulated by negative feedback, humoral, hormonal, and neural stimuli.
Hypothalamus and Pituitary Gland
- Hypothalamus-pituitary complex is the command center integrating neural and endocrine signals.
- Posterior pituitary stores and secretes ADH (water reabsorption by kidneys) and oxytocin (uterine contractions, milk ejection).
- Anterior pituitary produces GH, TSH, ACTH, FSH, LH, and PRL, each with specific target cells and functions.
- Secretion of anterior pituitary hormones is regulated by hypothalamic releasing and inhibiting hormones via the hypophyseal portal system.
Thyroid and Parathyroid Glands
- Thyroid gland regulates basal metabolism via T3 and T4 (synthesis requires iodine); calcitonin lowers blood calcium.
- Parathyroid glands secrete PTH, increasing blood calcium by stimulating osteoclasts, increasing kidney reabsorption, and activating vitamin D.
- Disorders include hypothyroidism (low T3/T4), hyperthyroidism (excess T3/T4), and goiter (thyroid enlargement).
Adrenal Glands
- Adrenal cortex produces mineralocorticoids (aldosterone), glucocorticoids (cortisol), and androgens.
- Adrenal medulla produces catecholamines (epinephrine, norepinephrine) for the fight-or-flight response.
- Short-term stress is managed by medulla; long-term stress by cortex (HPA axis).
- Disorders: Cushing's disease (excess cortisol), Addison's disease (cortisol deficiency).
Sensory Systems: Introduction and Function
- Somatic nervous system mediates voluntary movements via skeletal muscle and receives sensory input.
- Sensation is activation of sensory receptors; perception is central processing into meaningful patterns.
- Receptors are classified by structure (free nerve endings, encapsulated, specialized cells), location (exteroceptors, interoceptors, proprioceptors), and function.
Special Senses: Taste, Smell, Hearing, Balance, Vision
- Taste detects five modalities: sweet, salty, sour, bitter, umami, via papillae and taste buds.
- Olfactory receptors in nasal cavity detect odorants, with emotional memory connections through the limbic system.
- Ear structures transmit and amplify sound; cochlea and hair cells transduce sound waves to neural signals.
- Vestibular system (utricle, saccule, semicircular canals) detects head position and movement for balance.
- Eye anatomy supports phototransduction via rods (low light, grayscale) and cones (color, high acuity at fovea).
Key Terms & Definitions
- Hormone — chemical messenger secreted by endocrine glands affecting distant target cells.
- Endocrine gland — ductless tissue/organs secreting hormones into blood/lymph.
- Pituitary gland — master endocrine gland connected to hypothalamus; anterior and posterior lobes secrete distinct hormones.
- Thyroxine (T4)/Triiodothyronine (T3) — thyroid hormones regulating metabolism.
- Calcitonin — thyroid hormone lowering blood calcium.
- Parathyroid hormone (PTH) — increases blood calcium.
- Adrenal cortex/medulla — regions of adrenal gland producing steroid hormones and catecholamines.
- Photoreceptor — retinal cell transducing light; rods (low light), cones (color).
Action Items / Next Steps
- Review hormone pathways and feedback mechanisms.
- Study the anatomical locations and functions of major endocrine and sensory structures.
- Complete assigned readings on endocrine and sensory system disorders.