Hormone Transport and Endocrine System

Hormone Transport

• Hormones move from endocrine glands to target cells through the bloodstream
• They bind to receptors on target cells to trigger a response
• Endocrine glands secrete hormones directly into the blood, such as the thyroid and adrenal glands
• Exocrine glands release secretions through ducts to specific locations like sweat and salivary glands

Endocrine vs. Nervous System

• The endocrine system has a slower response but longer-lasting effects via hormones in the bloodstream
• The nervous system responds fast using electrical signals through neurons
• Both systems regulate and control body functions
• The nervous system uses electrical impulses for rapid control
• The endocrine system uses hormones for longer, sustained effects

General Functions of the Endocrine System

• The endocrine system regulates metabolism, growth, tissue function, mood, and reproductive processes

Hormone Categories

• Amino acid-based hormones, such as thyroid hormone and epinephrine, dissolve in water and don't need carrier proteins in the blood
• They generally cannot cross a plasma membrane directly
• They rely on receptors on the membrane to activate signaling pathways like second messengers
• Steroid hormones, like cortisol and testosterone, dissolve in lipids and need carrier proteins for blood transport
• They can cross the plasma membrane and bind to intracellular receptors, affecting gene expression and protein synthesis

Interaction with Target Cells

• Lipid-soluble hormones diffuse through the plasma membrane and bind to intracellular receptors, which affects gene expression
• Water-soluble hormones bind to surface receptors on the cell membrane, triggering internal signaling pathways that alter the cell's function

Hormone Regulation

• Hormonal regulation occurs when one hormone triggers the release of another
• Humoral regulation occurs when changes in blood levels of ions or nutrients affect hormone secretion
• Neural regulation occurs when nerve signals stimulate hormone release
• In negative feedback, a hormone's secretion is inhibited by its own effects

Factors Affecting Target Cell Activation

• Hormone concentration determines the strength of the response in target cells
• Target cells can change the number of receptors in response to hormone levels
• Higher binding affinity between hormone and receptor leads to a more potent effect

Hypothalamus and Pituitary Gland

• The hypothalamus regulates the pituitary gland, which is the "master gland"
• The posterior pituitary stores and releases ADH and oxytocin, originates in hypothalamus
• The anterior pituitary produces its own hormones under hypothalamic control through the portal system
• The portal system is made of blood vessels connecting the hypothalamus to the anterior pituitary for direct hormone signaling
• Releasing and inhibiting hormones from the hypothalamus regulate the anterior pituitary

Posterior Pituitary Hormones

• Antidiuretic hormone (ADH or vasopressin) targets kidneys to increase water reabsorption
• Oxytocin targets the uterus to stimulate contractions and mammary glands for milk ejection

Anterior Pituitary Hormones

• Thyroid Stimulating Hormone (TSH) stimulates the thyroid to release thyroid hormones
• Prolactin (PRL) stimulates milk production in mammary glands
• Follicle-Stimulating Hormone (FSH) stimulates egg and sperm production
• Luteinizing Hormone (LH) stimulates ovulation in females and testosterone production in males, along with FSH during reproduction
• Adrenocorticotropic Hormone (ACTH) stimulates the adrenal cortex to release corticosteroids like cortisol
• Growth Hormone (GH) stimulates growth and cell division in tissues
• TSH, FSH, LH, and ACTH, Tropic hormones, regulate hormone release from other endocrine glands

Growth Hormone Disorders

• Gigantism is excess GH during childhood, causing abnormal growth
• Acromegaly is excess GH in adulthood, causing enlarged extremities and facial features
• Pituitary dwarfism is GH deficiency during childhood, resulting in short stature

Thyroid Gland

• The thyroid gland is in the neck, just below the Adam's apple
• Follicular cells produce thyroid hormones (T3 and T4)
• Parafollicular cells produce calcitonin
• Colloid stores thyroid hormones before release
• Iodide synthesizes thyroid hormones and a deficiency causes goiter
• T3 and T4 regulate metabolism, energy use, and growth
• Calcitonin lowers blood calcium levels by inhibiting osteoclast activity.
• When thyroid hormone levels are low, the hypothalamus releases TRH, which stimulates the pituitary to release TSH, stimulating the thyroid to produce more T3 and T4
• High levels of T3 and T4 inhibit TRH and TSH release

Reproductive System

• Gonads are testes in males and ovaries in females, producing gametes and sex hormones
• Gametes are sperm in males and oocytes in females that combine during fertilization to form a zygote
• Accessory reproductive organs include the uterus, vagina, epididymis, and vas deferens helping in gamete transportation and nurturing
• Sex hormones are testosterone in males and estrogen in females
• Testosterone promotes male characteristics, spermatogenesis, and libido
• Estrogen promotes female secondary sex characteristics, regulates the menstrual cycle, and supports pregnancy
• The hypothalamus releases GnRH to stimulate the pituitary gland to secrete FSH and LH
• These hormones regulate gonadal function
• FSH stimulates gamete production (spermatogenesis in males and follicle development in females)
• LH stimulates hormone production from gonads (testosterone in males and estrogen/progesterone in females)

Meiosis

• Autosomes are 22 pairs of chromosomes that are the same in both males and females
• Sex chromosomes determine biological sex
• XX for females
• XY for males
• Somatic (body) cells are diploid (2n) and gametes (sperm and egg) are haploid (n)
• Mitosis is cell division for growth and repair, resulting in two identical daughter cells with a full set of chromosomes (2n)
• Meiosis reduces chromosome number by half to create gametes
• It involves two division rounds, resulting in four non-identical haploid cells
• Homologous chromosomes are pairs of chromosomes with similar shape, size, and genetic content, they originate with separate parents
• Sister chromatids are identical copies of a chromosome formed after DNA replication
• Replicated chromosomes are sister chromatids joined at the centromere
• Crossing over during meiosis I exchanges genetic material between homologous chromosomes, increases genetic diversity
• Meiosis I reduces chromosome number
• Meiosis II separates sister chromatids creating four non-identical haploid cells

Male Reproductive System

• The scrotum houses the testes outside the body to maintain optimal sperm production temperature
• Seminiferous tubules are the site of sperm production
• Sustentocytes (Sertoli cells) provide structural support to developing sperm
• Interstitial cells (Leydig cells) produce testosterone
• Spermatogenic cells produce sperm via spermatogenesis

Spermatogenesis

• Spermatogonia divide by mitosis to form primary spermatocytes
• Primary spermatocytes undergo meiosis I to form secondary spermatocytes
• Secondary spermatocytes undergo meiosis II to form spermatids
• Spermatids mature into functional sperm
• Sperm contains a head with genetic material
• The acrosome of the sperm cell is a cap on the head containing enzymes to help penetrate the egg
• The midpiece contains mitochondria for energy for motility
• The tail is a flagellum that enables sperm motility.

Path of Sperm

• Sperm is produced in the testes, then moves to the epididymis, vas deferens, ejaculatory duct, and urethra
• Sperm maturation and storage occurse in the epididymis
• The vas deferens transport sperm
• The ejaculatory duct mixes sperm with fluids
• The urethra is the final passage through the penis

Semen

• Seminal glands produce a fructose-rich fluid providing energy for sperm
• Bulbo-urethral glands secrete a lubricating fluid
• The prostate produces a fluid that helps activate sperm and neutralize the vaginal environment

Penis Structure

• The erectile tissue of the penisconsists of the corpus spongiosum and corpus cavernosum,which fills with blood to create rigidity during erection
• Erection is controlled by the parasympathetic nervous system
• Ejaculation is controlled by the sympathetic nervous system

Female Reproductive System

• Ligaments secure the ovaries in place
• The ovaries produce oocytes and hormones
• Uterine tubes transport eggs from the ovaries to the uterus with the infundibulum and fimbriae
• The uterus houses and nourishes the fetus with the endometrium which thickens for implantation and sheds during menstruation with it's functional and basal layer.
• The cervix is the opening to the uterus
• The vagina is the birth canal and site of sperm deposition
• Greater vestibular glands secrete mucus for lubrication during sexual intercourse

Oogenesis and Follicle Structure

• The oocyte is the egg cell
• Granulosa cells surround the oocyte and produce estrogen
• The antrum is is a fluid-filled cavity that forms during follicle maturation
• The corona radiata is a layer of granulosa cells surrounding the oocyte

Oogenesis

• Oogonia are stems cells in the ovaries
• Primary oocytes form before birth
• Secondary oocytes are formed at ovulation
• Ovulation is the release of the secondary oocyte
• The corpus luteum forms from the ruptured follicle after ovulation and secretes progesterone
• The corpus albicans is a degenerated form of the corpus luteum if fertilization doesn't occur

Uterine and Ovarian Cycles

• The menstrual phase sheds the functional layer (menstruation)
• The proliferative phase rebuilds the endometrium with estrogen
• The secretory phase is where the endometrium becomes ready for implantation with progesterone
• FSH and LH promote follicle maturation and ovulation

Hormones travel via the bloodstream to target cells, binding to receptors to initiate responses. The endocrine system's effects are slower but longer-lasting compared to the nervous system. It regulates metabolism, growth, mood, and reproduction.