Bio 1106 Unit 3

Three types of animal skeletons

Hydrostatic, exoskeletons, endoskeletons

Hydrostatic skeleton definition

Fluid‑filled cavity surrounded by muscles enabling movement

Animals with hydrostatic skeletons

Soft‑bodied terrestrial and aquatic invertebrates

Animals with exoskeletons

Arthropods

Animals with endoskeletons

Echinoderms and vertebrates

Main limitation of exoskeletons

They restrict growth

Functions of exoskeletons

Protection, muscle attachment, rigid support

Functions of endoskeletons

Internal support, muscle attachment, organ protection

Composition of bone

Collagen (flexibility) + hydroxyapatite (rigidity)

Cartilage tissue characteristics

Tough, flexible, avascular connective tissue

Cells that maintain cartilage

Chondrocytes

Osteoblasts

Cells that build bone

Osteocytes

Cells that maintain bone

Osteoclasts

Cells that break down bone

Haversian system

Structural unit of compact bone housing blood vessels and nerves

Intramembranous bone development

Bone forms within connective tissue (flat bones)

Endochondral bone development

Bone replaces a cartilage model

Bone remodeling

Balance of osteoblasts (build) and osteoclasts (break down)

Smooth muscle

Involuntary, internal organs

Cardiac muscle

Involuntary, contracts as a unit, heart

Skeletal muscle

Voluntary, attached to bones

Sarcomere

Smallest functional unit of muscle contraction

Myofibrils

Bundles of myofilaments responsible for contraction

Striations

Alternating dark/light bands in skeletal muscle

ATP binding to myosin

Causes myosin to release actin

ATP → ADP + Pi

Cocks the myosin head

Myosin binds actin

Cross‑bridge formation

Power stroke

Myosin pulls actin toward sarcomere center

New ATP binding

Myosin detaches from actin

Rigor mortis cause

No ATP to detach myosin from actin

Low Ca²⁺

Tropomyosin blocks actin binding sites

High Ca²⁺

Ca²⁺ binds troponin, moves tropomyosin, allows contraction

Sliding filament theory

Actin and myosin slide; filaments do not shorten

Acetylcholine (ACh)

Neurotransmitter at NMJ

Motor end plate

Muscle membrane region with ACh receptors

Na⁺ influx

Causes muscle depolarization

T‑tubules

Carry depolarization deep into muscle fiber

Sarcoplasmic reticulum

Stores and releases Ca²⁺

Motor unit

One motor neuron + all muscle fibers it innervates

Recruitment

Activating more motor units to increase force

Muscle twitch

Single contraction‑relaxation event

Summation

Multiple twitches combine to increase force

Incomplete tetanus

Sustained, powerful contraction with partial relaxation

Complete tetanus

Maximum tension, no relaxation

Slow‑twitch fibers

Aerobic, many mitochondria, high myoglobin, fatigue‑resistant

Fast‑twitch fibers

Anaerobic, fewer mitochondria, low myoglobin, fatigue quickly

Calorie (kilocalorie)

Unit of energy; amount needed to raise 1 kg of water by 1°C

Basal metabolic rate (BMR)

Minimum energy required at rest

Proteins

Provide amino acids for building tissues and enzymes

Essential amino acids

Amino acids that must be obtained from diet

Number of amino acids required by humans

11 of the 20 must come from diet

GI tract

Tubular digestive pathway from mouth to anus

Accessory organs

Liver, pancreas, gallbladder, salivary glands

Mucosa

Innermost layer responsible for secretion, absorption, protection

Epithelium of mucosa

Stratified squamous (mouth, esophagus, anus) or simple columnar (stomach, intestines)

Lamina propria

Connective tissue with blood vessels, lymphatics, immune cells

Muscularis mucosae

Thin smooth muscle increasing surface area

Submucosa

Dense connective tissue with vessels, glands, and nerve plexus

Muscularis externa

Smooth muscle layers responsible for motility

Myenteric plexus

Nerve network controlling gut movement

Serosa

Slippery membrane covering abdominal organs

Adventitia

Connective tissue covering organs outside peritoneum

Function of teeth

Mechanical digestion (mastication)

Bird digestion

No teeth; use two‑chambered stomach

Saliva components

Water, mucus, amylase, antibacterial compounds

Bolus

Chewed mass of food ready to swallow

Swallowing

Starts voluntary, continues involuntarily

Esophagus

Muscular tube connecting pharynx to stomach

Peristalsis

Wave‑like contractions moving food through GI tract

Gastric juice components

Mucus, HCl, pepsin

Pepsinogen

Inactive form of pepsin

Three regions of small intestine

Duodenum, jejunum, ileum

Primary site of digestion and absorption

Small intestine

Villi and microvilli

Increase surface area for absorption

Brush border enzymes

Complete digestion of proteins, carbs, fats

Chylomicrons

Fat transport particles entering lymphatic system

Pancreas

Major digestive organ producing enzymes and bicarbonate

Trypsin & chymotrypsin

Break proteins into smaller peptides

Pancreatic amylase

Breaks polysaccharides into sugars

Lipase

Breaks fats into fatty acids and monoglycerides

Bicarbonate

Neutralizes acidic chyme

Liver functions

Detoxification, protein synthesis, glycogen storage, bile secretion

Bile

Contains bile salts and pigments; emulsifies fats

Colon functions

Absorbs water, electrolytes, vitamin K; compacts feces

Rectum

Stores feces; contains two sphincters

Feces composition

Water, electrolytes, mucus, bacteria, bile pigments

Nonruminant herbivore

Simple stomach, large cecum

Ruminant herbivore

Four‑chambered stomach with rumen

Insectivore

Short intestine, no cecum

Carnivore

Short intestine and colon, small cecum

Gastrin

Released in response to protein; stimulates stomach secretions

CCK

Released in response to fatty chyme; stimulates gallbladder & pancreas

GIP

Released in response to fatty chyme; inhibits stomach activity

Secretin

Released in response to acid; stimulates pancreatic bicarbonate

Leptin

Long‑term appetite suppression; released by fat cells

Insulin

Long‑term appetite suppression; released by pancreas

Ghrelin

Short‑term appetite stimulant; released by stomach

CCK

Short‑term appetite reduction; released by duodenum

Dr. William Beaumont

Beaumont discovery 1 — Demonstrated chemical digestion using gastric juice

Beaumont discovery 2 — Identified stomach motility and churning

Beaumont discovery 3 — Documented digestion rates of different foods

Beaumont significance — Helped establish experimental physiology

What percentage of carbon dioxide is dissolved in plasma?

About 8% is dissolved in plasma.