Cram sheet
30 points- Four levels of organization, in order: cells → tissues → organs → organ systems. A tissue is a group of similar cells with a common embryonic origin doing one job; an organ combines several tissue types into one functional unit; an organ system is organs cooperating on a major function. Watch Introduction to Anatomy & Physiology: Crash Course Anatomy & Physiology #1 on YouTube, from CrashCourse
- The four primary tissue types are epithelial, connective, muscle, and nervous. Every exam version of this chapter asks for these four. Watch Tissues, Part 1: Crash Course Anatomy & Physiology #2 on YouTube, from CrashCourse Watch The Four Types of Tissues - Epithelial, Connective, Nervous and Muscular on YouTube, from Armando Hasudungan
- Sponges have no true tissues. Cnidarians are diploblastic (ectoderm + endoderm only). Everything else is triploblastic — the added mesoderm is what makes so many tissue types possible.
- Epithelium is classified by two criteria: number of layers (simple = one, stratified = two or more) and cell shape (squamous = flat, cuboidal = cube, columnar = tall). Watch Tissues, Part 2 - Epithelial Tissue: Crash Course Anatomy & Physiology #3 on YouTube, from CrashCourse
- Know these epithelium locations cold: simple squamous = alveoli and capillaries; simple cuboidal = kidney tubules, glands, ovary surface; simple columnar = stomach and intestine lining; pseudostratified columnar = respiratory tract (ciliated, mucus); stratified squamous = skin epidermis and mouth lining. Watch Tissues, Part 2 - Epithelial Tissue: Crash Course Anatomy & Physiology #3 on YouTube, from CrashCourse
- Pseudostratified is a trick: it is really one layer — every cell touches the basement membrane, but only some reach the free surface.
- Epithelium has almost no extracellular material, is held by tight junctions and desmosomes, sits on a basement membrane, has a free apical surface, and is avascular — no blood vessels enter it, so nutrients diffuse in from vessels in the connective tissue below. It also has a high mitotic rate, which is why wounds close fast.
- Glands are epithelium built to secrete. Exocrine glands secrete through ducts (sweat, salivary). Endocrine glands secrete into the blood (thyroid, pituitary, pancreatic islets). A goblet cell is a unicellular exocrine gland.
- Connective tissue is the mirror image of epithelium: few cells, huge extracellular matrix, richly vascularized, all from mesoderm. It splits into connective tissue proper (loose and dense) and special connective tissues (cartilage, bone, blood). Watch Tissues, Part 3 - Connective Tissues: Crash Course Anatomy & Physiology #4 on YouTube, from CrashCourse
- Matrix = protein fibers + ground substance. The three fibers are collagen (support meshwork), elastin (elasticity), and reticulin (props up the collagen network). Fibroblasts secrete this matrix; loose connective tissue also holds mast cells, macrophages, and adipose cells.
- Dense regular = collagen in parallel → tendons (muscle to bone) and ligaments (bone to bone). Dense irregular = collagen in many directions → organ capsules and sheaths. Watch Tissues, Part 4 - Types of Connective Tissues: Crash Course Anatomy & Physiology #5 on YouTube, from CrashCourse
- Cell names by tissue: chondrocyte = cartilage (sits in a lacuna), osteocyte = bone (connected by canaliculi), fibroblast = connective tissue proper, erythrocyte / leukocyte = blood. Watch Tissues, Part 4 - Types of Connective Tissues: Crash Course Anatomy & Physiology #5 on YouTube, from CrashCourse
- Cartilage has no blood vessels — chondrocytes are fed by diffusion, which only works because the matrix stays hydrated and uncalcified. Bone matrix is calcified (calcium phosphate), so osteocytes need central canals carrying vessels.
- Blood is connective tissue because its cells are suspended in an enormous extracellular matrix — the fluid plasma. Watch Tissues, Part 4 - Types of Connective Tissues: Crash Course Anatomy & Physiology #5 on YouTube, from CrashCourse
- Three muscle types: smooth (visceral, involuntary, spindle-shaped, one nucleus, unstriated), skeletal (voluntary, striated, long fibers, multinucleate from cell fusion), cardiac (striated, heart only, one nucleus per cell, joined by intercalated disks that are gap junctions). Watch Types of Tissue Part 3: Muscle Tissue on YouTube, from Professor Dave Explains Watch Muscles, Part 1 - Muscle Cells: Crash Course Anatomy & Physiology #21 on YouTube, from CrashCourse
- The defining muscle trait is converting chemical energy into mechanical force, and myosin appeared first in sponges, before true muscle existed. Cardiac muscle is self-exciting: an excised frog heart keeps beating in a nutrient bath (Fig 41.7), and the nervous system only sets the rate.
- Nervous tissue = neurons (conduct impulses) + neuroglia (support, nourish, protect, regulate — they do not conduct). Neuron parts: cell body, dendrites (in), axon (out). Watch The Nervous System, Part 1: Crash Course Anatomy & Physiology #8 on YouTube, from CrashCourse
- The 11 organ systems: nervous, endocrine, skeletal, muscular, digestive, circulatory, respiratory, urinary, integumentary, lymphatic/immune, reproductive. Five functional groups: communication and integration; support and movement; regulation and maintenance; defense; reproduction and development. Watch Human Body Systems Overview (Updated 2024) on YouTube, from Amoeba Sisters
- Homeostasis = the dynamic constancy of the internal environment. Dynamic because values oscillate around a set point rather than sit still. Watch Homeostasis and Negative/Positive Feedback on YouTube, from Amoeba Sisters
- A negative feedback loop has four parts in order: stimulus → sensor → integrating center → effector → response, and the response feeds back to shut the loop down. Watch Physiological concept of positive and negative feedback | Behavior | MCAT | Khan Academy on YouTube, from khanacademymedicine Watch Homeostasis and Negative/Positive Feedback on YouTube, from Amoeba Sisters
- Antagonistic effectors = two opposing effectors, each limited by negative feedback, giving push-pull control (furnace + AC; shivering + sweating). Finer control than one effector switching on and off. Watch Homeostasis - negative and positive feedback (thermoregulation and lactation) on YouTube, from Armando Hasudungan
- Positive feedback pushes a value farther from set point. It does not maintain homeostasis. Only two examples to know: blood clotting and uterine contractions in childbirth (oxytocin loop, Fig 41.12). Watch Physiological concept of positive and negative feedback | Behavior | MCAT | Khan Academy on YouTube, from khanacademymedicine
- Q10 = R(T+10)/R(T). Roughly 2 for enzyme reactions, 2–3 for whole-organism metabolism, and near 1 in a few temperature-insensitive intertidal invertebrates.
- Four heat-transfer routes: radiation (no contact needed), conduction (direct contact), convection (moving fluid or air), evaporation (loss only, uses water high heat of vaporization). Watch Thermoregulation on YouTube, from Bozeman Science
- Endotherm vs ectotherm is about the heat source — do you make your own heat metabolically? Homeotherm vs poikilotherm is about constancy of temperature. The old terms warm-blooded and cold-blooded are inaccurate and outdated. Watch Thermoregulation on YouTube, from Bozeman Science
- Ectotherms still thermoregulate — by behavior (basking lizards, sun-orienting butterflies, shivering moths) and even by countercurrent heat exchange in tuna and some sharks. A lizard needs only about 10% of the energy a same-sized mouse needs. Watch Thermoregulation on YouTube, from Bozeman Science
- Endotherm cold response: vasoconstriction, shivering thermogenesis, epinephrine from the adrenal medulla and TSH → thyroxine to raise metabolism. Heat response: vasodilation, sweating or panting, and suppression of metabolism-boosting hormones. Watch Homeostasis - negative and positive feedback (thermoregulation and lactation) on YouTube, from Armando Hasudungan
- Nonshivering thermogenesis happens in brown adipose tissue (BAT), where UCP1 leaks protons and uncouples electron transport from ATP synthesis — the energy comes out as heat instead of ATP.
- The hypothalamus is the integrating center for body temperature, with a heat-losing center and a heat-promoting center; set point = 37 °C (98.6 °F). Fever means pyrogens raise that set point — bacterial endotoxins and substances from white blood cells are pyrogens, and the higher temperature suppresses bacterial growth, so fever is a defense.
- Torpor = reduced metabolic rate and body temperature (hummingbirds drop up to 25 °C at night). Hibernation = deep torpor for weeks to months, up to 20 °C below set point. Bears do not truly hibernate — they enter a winter sleep with only a few degrees of drop.