Digestive System Practice Flashcards

Flashcards reviewing the structure and functions of the human digestive system, dental characteristics, salivary glands, and digestive enzymes based on textbook lecture notes.

What is digestion as defined in the textbook?

Digestion is the breakdown of naturally occurring foodstuffs into diffusable form, or any change which makes food soluble and of such chemical nature that it can be absorbed readily through living membranes.

What is the optimum temperature range for human digestive enzymes?

Enzymes act best within a narrow temperature range usually between $35^\text{o}\text{C}$ and $40^\text{o}\text{C}$, which is called the optimum temperature.

What is the total length of the human alimentary canal?

The alimentary canal is a muscular tube that is about $9\text{ metres}$ long.

What are the structural features and functions of incisors?

Incisors are the four front teeth in the centre of each jaw. They have broad and sharp chisel-like cutting edges used for biting and cutting.

What are the structural features and functions of canine teeth?

Canines are one on either side of the incisors in each jaw. They are conical and sharply pointed for holding and tearing food.

What are premolars and why are they called bicuspids?

Premolars are two on each side in each jaw next to the canines. They are called bicuspids because each premolar has two hill-like projections or cusps on its surface. They help in grinding and crushing food.

What are wisdom teeth and when do they typically appear?

Wisdom teeth are the last molars on each side in each jaw. They appear last at an age of about $17\text{--}20\text{ years}$ when the human body is reaching maturity.

What is the difference between heterodont and homodont dentition?

Heterodont dentition refers to teeth of different shapes performing different functions (e.g., humans and mammals), whereas homodont dentition refers to teeth that are all similar in shape (e.g., lizards and frogs).

What is the number and timeline of temporary (milk) teeth in humans?

The temporary (deciduous) set consists of $20\text{ teeth}$ (all types except premolars). They start growing around $7\text{--}8\text{ months}$ of age, are complete by about $2\text{ years}$, and are completely replaced by permanent teeth by about $12\text{ years}$ of age.

What are the dental formulas for a human child, an adolescent, and an adult?

Human child (up to ~2 years): $\frac{2,1,0,2}{2,1,0,2} = 20$\nHuman adolescent (up to ~17-20 years): $\frac{2,1,2,2}{2,1,2,2} = 28$\nHuman adult: $\frac{2,1,2,3}{2,1,2,3} = 32$

What is enamel and what makes it unique?

Enamel (or "ivory") is the material covering the crown of the tooth and is the hardest substance in the human body.

What is the function and location of cementum in a tooth?

Cementum is a bone-like structure covering and fixing the root of the tooth in position within the jaw socket.

What are the three pairs of salivary glands and their locations?

1. Parotid glands: located just in front of and beneath each ear.\n2. Submandibular glands: lying close to the inner side of the lower jaw on each side.\n3. Sublingual glands: located below the tongue.

What is the daily volume and pH of human saliva?

Humans produce about $1000\text{--}1500\text{ ml}$ of saliva daily. It is a very slightly acidic fluid with a pH of $6.8$.

How does salivary amylase (ptyalin) affect starch?

Ptyalin (salivary amylase) breaks down starch into the disaccharide maltose: $\text{Starch} \xrightarrow{\text{Ptyalin}} \text{Maltose}$

What prevents swallowed food from entering the nasal cavity and windpipe?

The soft palate closes the opening to the nasal passage, and the larynx moves upward so that a flap called the epiglottis covers the glottis (opening of the windpipe).

What is peristalsis?

Peristalsis is the wave of constrictions caused by the circular muscles of the gut pushing food along, followed by relaxation as the wave passes.

What is the food capacity of an adult stomach and what are its two sphincters?

An average adult stomach can hold $2\text{ to }3\text{ litres}$ of food. Its opening from the oesophagus is guarded by the cardiac sphincter, and its opening into the duodenum is guarded by the pyloric sphincter.

What triggers vomiting (antiperistalsis)?

When the stomach is overloaded or disturbed, the cardiac sphincter opens and a reverse wave of muscular contraction (antiperistalsis) throws the stomach contents out through the mouth.

What are the two main functions of hydrochloric acid (HCl) in gastric juice?

(i) It kills germs that may have entered along with food.\n(ii) It converts inactive pepsinogen into active pepsin to act on proteins.

How does pepsin digest proteins in the stomach?

Pepsin digests proteins (about $20\%$ of total proteins) into peptides.

What is the function of rennin and in whom is it found?

Rennin converts soluble milk protein (casein) into insoluble paracasein. It is found only in babies and not in adult humans.

What are the three sub-regions of the small intestine and their dimensions?

1. Duodenum: short upper part next to the stomach ($12\text{ finger widths}$ in length).\n2. Jejunum: next short region of about $2\text{ metres}$.\n3. Ileum: region of about $4\text{ metres}$.

What are villi and how do they aid in absorption?

Villi are tiny finger-like projections in the inner lining of the ileum that increase the inner surface area by nearly $8\text{ times}$ that of the outer body surface to facilitate food absorption.

Where is bile produced, where is it stored, and what are its functions?

Bile is produced in the liver and temporarily stored in the gall bladder. It contains sodium bicarbonate ($\text{NaHCO}_3$) to neutralize acidic chyme making it alkaline, and bile salts to emulsify fats into tiny droplets.

What are the three enzymes in pancreatic juice and their actions?

1. Amylopsin (pancreatic amylase): digests leftover starch into maltose.\n2. Trypsin: converts remaining proteins and polypeptides into smaller peptides and amino acids.\n3. Steapsin: splits emulsified fats into fatty acids and glycerol.

How is inactive trypsinogen activated in the duodenum?

Inactive trypsinogen is activated into active trypsin by the enzyme enterokinase (enteropeptidase), which is secreted by the inner lining of the duodenum.

What are the enzymatic reactions carried out by intestinal juice?

(i) Peptides $\xrightarrow{\text{Erepsin}}$ Amino acids\n(ii) Maltose $\xrightarrow{\text{Maltase}}$ Glucose\n(iii) Sucrose $\xrightarrow{\text{Sucrase}}$ Glucose + Fructose\n(iv) Lactose $\xrightarrow{\text{Lactase}}$ Glucose + Galactose\n(v) Emulsified fat $\xrightarrow{\text{Lipase}}$ Fatty acids + Glycerol

How do absorption pathways differ between simple sugars/amino acids and fatty acids/glycerol?

Amino acids and simple sugars pass through villi epithelium into blood capillaries to reach the liver via the hepatic portal vein. Fatty acids and glycerol are absorbed into lymph vessels (lacteals) to enter the lymphatic system.